Image processing subroutines

Patrik and myself are glad to submit the new pull request of image_processing.{c,h} and image_processing.pyx  (Cython binding), check_image_processing.c (Check unit tests) and also Python tests test_lena.py. In short we fixed few bugs and tested the image_processing subroutines, some of which were not used, but might become useful with the new Python bindings. In addition, we added two new subroutines that are, to our opinion, provide better filter results and treat image borders appropriately. 

Please, build and test it on your platform and provide your feedback. Note: this pull request has to be pulled after the epi.{c,h} and other pull requests are approved. 

Patrik, Alex