Removal of grib hindcast patch and other bugfixes to osx recipe

The PR changes the OS X recipe to:

1) use pip to install matplotlib as v1.2.0 is now in pypi.
2) remove the grib negative forecast time patch as it is no longer necessary (see https://github.com/SciTools/iris/pull/174)

This PR also includes a number of bugfixes based on feedback from a user.