Integrated unit testing framework with scons on Linux.

I needed this to make sure that BKE_copy_images works properly,
probably will be useful in future.

Using Check framework (http://check.sourceforge.net/doc/check.html/index.html).

WITH_BF_UNIT_TEST option builds 'alltest' program under [BUILDDIR]/bin, 
which, when executed, runs unit tests, currently only 1.

Example output:
----------------------------------------------------------------------
Running suite(s): Image
0%: Checks: 1, Failures: 1, Errors: 0
tests/alltest.c:74:F:Core:test_copy_images:0: Expected //bar/image.png to be translated to /tmp/bar/image.png, got /tmp/bar/image.pn.
----------------------------------------------------------------------

Spent lots of time (a couple of days actually :) to figure out how to
link the test program with Blender libraries. As it turned out there
are circular dependencies among Blender libraries. GCC by default
doesn't expect circular dependencies - dependant libs should precede
libs they depend on.

The magical --start-group linker option helped to solve this
(http://stephane.carrez.free.fr/doc/ld_2.html#IDX122).

Also:

- added bpy.util module. bpy.sys.* functions will move here later
- added bpy.util.copy_images that uses BKE_copy_images
- export_obj.py uses bpy.util.copy_images

source/blender/python/intern/bpy_interface.c

@@ -92,6 +92,9 @@ void BPY_update_modules( void )
 	PyObject *mod= PyImport_ImportModuleLevel("bpy", NULL, NULL, NULL, 0);
 	PyModule_AddObject( mod, "data", BPY_rna_module() );
 	PyModule_AddObject( mod, "types", BPY_rna_types() );
+	PyModule_AddObject( mod, "util", BPY_util_module() );
+
+	/* XXX this will move to bpy.util */
 	PyModule_AddObject( mod, "sys", BPY_sys_module() );
 }