It makes things more self contained (although you still need to
download FLTK itself), avoids the confusion of STR:s in varying
states, and allows us to refer to patches that aren't available
on an STR.
Added 'contrib' folder to store patches necessary to build external dependecies, distribution-specific packaging files, etc. Also added a delimiter to the end of the fltk patch script defined in BUILDING.txt to make it easier to parse this script out for automated builds.