Cpp source include fixes

[vspinu]

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Two improvements to srouce_cpp():

• Honor <basename>_types.h or <basename>_types.hpp (I included both extensions because editor support might be different for different extensions. And I feel it's cleaner to use hpp for cpp code). Fixes #216
• Add file's directory to the include path. (addresses most common use case of #246 without dealing with CPPFLAGS trickery)

[vspinu]

Re-add cleaning of _N.cpp suffixing logic originally done in #176 (4ef13b7) as per comment.