library build target to the .gyp file (not required by any executable yet). Fix
some build errors with SampleApp on Linux and Win32. Add a gyp_skia python
script which invokes gyp with the correct arguments, and is recursively callable
by the Makefile when skia.gyp is changed.
Review URL: http://codereview.appspot.com/4280069/
git-svn-id: http://skia.googlecode.com/svn/trunk@1007 2bbb7eff-a529-9590-31e7-b0007b416f81
