Reviving Codegen_C

In the examples I'm trying, gcc barfs on min and max operators.
Still investigating.
Demosaic reference comparison hacking
Merge branch 'master' of github.com:halide/Halide
Add support for writing TIFF as a debug file format.

Change separator for unique name counter from '.' to '#'
Merge branch 'master' of https://github.com/halide/Halide
Merge branch 'master' into nick-sandbox