Shrimp Shader Generator FLTK2 GUI (SVN)

- add 2 separate filters in the file browser tif,tiff and tex,tdl,tx.
- fix path/name was passed to the shader without quotes.

FIX: TIFF preview now works properly

ENH: uncommented Freddy's work on TIF file preview, it works for me

-fix crash when select a texture file using the new file dialog in block attribute.

- Fix a bug in preference dialog the rib selection choice wasn't apply
- Add file dialog for choosing image (for example environment map)
- I had the preview of tif and tdl images in the file dialog but the code it's commented for memory issues.
- Add libtiff in Sconstruct for supporting tif and tdl preview but the code it's commented as well.

FIX: RIB scenes were appended to the list each time the preference dialog was opened

-update usage section with information of the blending mode number for each mode

- New block in a new section call Layering :blend color ,blend two color using the selected blending mode

Added some fixes and comments to the Cook-Torrance model, and the microfacet distributions and shadowing/masking functions in their respective headers.

ENH: experimental array support (without the message passing stuff)