Fix proton build issue with debian jessie, as used on CI servers.

Debian 8 stable ships with gcc 4.9.2 and cmake 3.0.2.  Previously
the depends package used CMAKE_CXX_STANDARD to tell cmake to use
C++11, but the option requires cmakes 3.1+.  To resolve the issue
we now update relevant CMakeLists.txt and set CMAKE_CXX_FLAGS.

depends/packages/proton.mk

@@ -6,6 +6,9 @@ $(package)_sha256_hash=6ffd26d3d0e495bfdb5d9fefc5349954e6105ea18cc4bb191161d2774
 $(package)_dependencies=
 
 define $(package)_preprocess_cmds
+  sed -i '1i set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")' proton-c/bindings/cpp/CMakeLists.txt && \
+  sed -i '1i set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")' examples/cpp/CMakeLists.txt && \
+  sed -i '1i set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")' CMakeLists.txt && \
   sed -i.old 's/qpid-proton SHARED/qpid-proton STATIC/' proton-c/CMakeLists.txt && \
   sed -i.old 's/SASL/_DO_NOT_BUILD_SASL_/' proton-c/CMakeLists.txt && \
   sed -i.old 's/qpid-proton-core SHARED/qpid-proton-core STATIC/' proton-c/CMakeLists.txt && \
@@ -20,8 +23,7 @@ define $(package)_config_cmds
 endef
 
 define $(package)_build_cmds
-  cd build; $(MAKE) VERBOSE=1 all && \
-  cp CMakeCache.txt /tmp/CMakeCache.txt
+  cd build; $(MAKE) VERBOSE=1
 endef
 
 define $(package)_stage_cmds