fix setting of path to headers for msvc
fix setting of path to headers for msvc

fixed paths to the windows headers, i.e.
replaced '..' prefix, which doesn't make any
sense in the top-level CMakeLists.txt, by
'windows/', which is the place where these
files are actually located.

Also added missing include_directories()
command to use the previously set variable
(STP_INCL_COMM) at all. According to grep,
STP_INCL_COMM is not used anywhere else.

kyledewey/stp,kyledewey/stp,kyledewey/stp,kyledewey/stp,kyledewey/stp,kyledewey/stp