saga: 2.1.0

Updated SAGA GIS to the latest version.
Updated the dependencies list to include the appropriate IO and Projection libraries.
Marked up the makefiles to remove references to unsupported libraries.

This package requires a recent build of wxmac, which addresses this pull request:
https://github.com/mxcl/homebrew/pull/21179

Otherwise it will complain of missing wxWidget packages on 64-bit systems.