Search for cmake in /usr/local/bin

The update_libgit2 scripts search 'only' in the default PATH
for cmake.
I've installed cmake via brew in /usr/local/bin and Xcode's 
default PATH environment variable in the Run Script phase 
does not seem to include that by default. So just add it :-)

Besides that, add the scripts to the xcode project, so they are
easier to find.