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_util.h

@@ -81,4 +81,6 @@ int BPy_errors_to_report(struct ReportList *reports);
 struct bContext *BPy_GetContext(void);
 void BPy_SetContext(struct bContext *C);
 
+PyObject *BPY_util_module(void); 
+
 #endif