Remove 'ccache' from CXX variable before calling python build system.

Otherwise if CXX="ccache g++", then Python tries to build with just
"ccache" for some reason, and breaks.
Add a check for C++11 compiler flags.

Necessary since C++ headers use some C++11 features.
(Copied from liblo's configure.ac)
Make variable liblo_CXXFLAGS doesn't exist, pkg-config only supports CFLAGS.
Add some missing C++ headers in mapper_cpp.h.
Add 'const' qualifier to get() methods, allowing use of C++11 for-iterators.
Merge remote-tracking branch 'steve/master'
C++: Fixed ptr bug