add missing set/get fileapi on context functions

git-svn-id: http://svn.osgeo.org/metacrs/proj/trunk/proj@2354 4e78687f-474d-0410-85f9-8d5e500ac6b2
Remove internal declaration of PROJ_LIB - makes it hard to not have a value

git-svn-id: http://svn.osgeo.org/metacrs/proj/trunk/proj@2355 4e78687f-474d-0410-85f9-8d5e500ac6b2