bdb 6.X was released under the AGPL, which is incompatible with MIT-licensed
software (the result must be licensed under AGPL). bdb 5.X uses the same license
as bdb 4.8, and thus retains the same compatibility as in upstream Bitcoin.
Thanks to Luke-Jr for raising this issue.
AC_ARG_WITH([incompatible-bdb],[AS_HELP_STRING([--with-incompatible-bdb], [allow using a bdb version other than 6.2])],[
AC_MSG_WARN([Found Berkeley DB other than 6.2; wallets opened by this build will not be portable!])
AC_ARG_WITH([incompatible-bdb],[AS_HELP_STRING([--with-incompatible-bdb], [allow using a bdb version other than 5.3])],[
AC_MSG_WARN([Found Berkeley DB other than 5.3; wallets opened by this build will not be portable!])
],[
AC_MSG_ERROR([Found Berkeley DB other than 6.2, required for portable wallets (--with-incompatible-bdb to ignore or --disable-wallet to disable wallet functionality)])
AC_MSG_ERROR([Found Berkeley DB other than 5.3, required for portable wallets (--with-incompatible-bdb to ignore or --disable-wallet to disable wallet functionality)])