Updated PerkTutor extension: Added Subversion_SVN_EXECUTABLE and GIT_EXECUTABLE variables.

Compare link: https://github.com/PerkTutor/PerkTutor/compare/86f23be65842564a88a62a55c7d5e0e4a05bf02f...d7ad1d866934dd305b3dd7fb4a66a40fb251367d