STYLE: Simplify CMake code re-using already set variable

As of r16822, the variable PYTHON_LIBRARY_PATH is set in the top-level
CMakeLists.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21945 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix hook error specific Git bash/GUI using an old version of BASH.

Thanks Sankhesk for his help.

See http://www.na-mic.org/Bug/view.php?id=3086
Fixes #3086

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21946 3bd1e089-480b-0410-8dfb-8563597acbee