Fixes for clang++ (3.4) and g++ (4.8.3) on Linux

+ Removed -stdlib compiler flag from CMakeLists.txt as newer compilers
do not recognize this flag on Linux. May be more checks are needed
before setting CMAKE_CXX_FLAGS.
+ #Included <cstring> and <climit> in src/MsgPack.cpp and
src/Socket.cpp as mem*** functions are no more available in std:: due to
removal of redundant #includes in std library headers.