Explicitly set BR in each halving interval

This extremely important consensus-changing code takes into account
that with our new 75s block time, which gives us twice as many blocks
per day, we must divide our block reward by two in the next
halving interval, becoming 3.125 HUSH per block insted of 6.25 HUSH
under the old rules of 150s blocks.

Subsequent halving intervals do not change block times, and so they
follow the normal pattern of halving.

This commit has a number of rough edges:
        * Final BR height is still incorrect
        * Due to above, exact number of halvings is unknown under new
          75s blocktime

src/komodo_bitcoind.h

@@ -1250,15 +1250,24 @@ uint64_t komodo_commission(const CBlock *pblock,int32_t height)
         //fprintf(stderr,"ht.%d nSubsidy %.8f prod %llu\n",height,(double)nSubsidy/COIN,(long long)(nSubsidy * ASSETCHAINS_COMMISSION));
         commission = ((nSubsidy * ASSETCHAINS_COMMISSION) / COIN);
 
+        // Do not change this code unless you really know what you are doing.
+        // Here Be Dragons! -- Duke Leto
         if (ishush3) {
             // TODO: Calculate new BR_END based on 75s block time!!! 2X old BR_END is a rough estimate, not exact!
             int32_t starting_commission = 125000000, HALVING1 = GetArg("-z2zheight",340000),  INTERVAL = 840000, TRANSITION = 129, BR_END = 2*5422111;
+            // TODO: how many halvings will we have given new 75s blocktime?
+            int32_t commisions[] = {starting_commision, 3125000000, 1562500000, 781250000, 390625000,
+                                    195312500, 97656250, 48828125, // these are exact
+                                    24414062, 12207031, 6103515 // these have deviation from ideal BR
+                                    // Just like BTC, BRs in the far future will be slightly less than
+                                    // they should be because exact values are not integers, causing
+                                    // slightly less coins to be actually mined
+            };
             // HUSH supply curve cannot be exactly represented via KMD AC CLI args, so we do it ourselves.
             // You specify the BR, and the FR % gets added so 10% of 12.5 is 1.25
             // but to tell the AC params, I need to say "11% of 11.25" is 1.25
             // 11% ie. 1/9th cannot be exactly represented and so the FR has tiny amounts of error unless done manually
 
-
             if( height > HALVING1) {
                 // Block time going from 150s to 75s (half) means the interval between halvings
                 // must be twice as often, i.e. 840000*2=1680000
@@ -1271,25 +1280,25 @@ uint64_t komodo_commission(const CBlock *pblock,int32_t height)
             if (height < TRANSITION) {
                 commission = 0;
             } else if (height < HALVING1) {               // before 1st Halving @ Block 340000 (Nov 2020)
-                commission = starting_commission;
+                commission = commisions[0];
             } else if (height < HALVING1+1*INTERVAL) {    // before 2nd Halving @ Block 2020000
-                commission = starting_commission / 2;
+                commission = commisions[1];
             } else if (height < HALVING1+2*INTERVAL) {    // before 3rd Halving @ Block 3700000
-                commission = starting_commission / 4;
+                commission = commisions[2];
             } else if (height < HALVING1+3*INTERVAL) {    // before 4th Halving @ Block 5380000
-                commission = starting_commission / 8;
+                commission =  commisions[3];
             } else if (height < HALVING1+4*INTERVAL) {    // before 5th Halving @ Block 7060000
-                commission = starting_commission / 16;
+                commission =  commisions[4];
             } else if (height < HALVING1+5*INTERVAL) {    // before 6th Halving @ Block 8740000
-                commission = starting_commission / 32;
+                commission = commisions[5];
             } else if (height < HALVING1+6*INTERVAL) {    // before 7th Halving @ Block 10420000
-                commission = starting_commission / 64;
+                commission = commisions[6];
             } else if (height < HALVING1+7*INTERVAL) {    // before 8th Halving @ Block 12100000
-                // Block reward will go to zero between 7th+8th halvings, ac_end may need adjusting
-                commission = starting_commission / 128;
+                // TODO: Still true??? Block reward will go to zero between 7th+8th halvings, ac_end may need adjusting
+                commission = commisions[7];
             } else if (height < HALVING1+8*INTERVAL) {    // before 9th Halving @ Block 13780000
                 // BR should be zero before this halving happens
-                commission = starting_commission / 256;
+                commission = commisions[8];
             }
             // Explicitly set the last block reward
             // BR_END is the block with the last non-zero block reward, which overrides