Mac / COCOA : Imbuf

Mac / COCOA : Imbuf

- replace libtiff by calls to Cocoa services to load/save tiff files
(Libtiff, dynamically linked is not distributed with OS X, and would have had to be shipped for all four architectures)

The imb_cocoaLoadImage & imb_cocoaSaveImage are generic towards the bitmap format, and thus can handle TIFF, GIF, JPG, JP2000, BMP and raw camera formats (read-only for these), even if today only TIFF is used as the other formats are already handled.

- CMake updated
- scons updated (Thx to Jens Verwiebe)