Make Visual Studio Build Process A Bit Simpler

Make Visual Studio Build Process A Bit Simpler

Add some flexibility in the property sheets for one building GTK+ that it
also searches for a settable installation path of Python, in addition to
searching the PATH for an installation of the Python interpretor.  This
currently defaults to Python 2.7.x, which is normally installed in
c:\python27 on Windows by default.  Also tell people in the README.txt's
for the Visual Studio builds