don't include .git files in source packages

the existing ".git/" rule only filters out .git directories,
but as we have submodules now, we have to filter out .git files too.

Author: vuvova

cmake/cpack_source_ignore_files.cmake

@@ -15,6 +15,7 @@
 
 SET(CPACK_SOURCE_IGNORE_FILES
 \\\\.git/
+\\\\.git$
 \\\\.gitignore$
 \\\\.gitattributes$
 CMakeCache\\\\.txt$