patch against original libpgf 6.11.24 to :
- Handle properly OpenMP depending of compiler/OS (inspired from libraw.org).
- Include only one omp.h instance in PGFplatform.h
- Support no OpenMP availability (else libpgf do not compile without OpenMP).
This patch must be included in next stable libpgf.

Raphael, i recommend too to change EOL as Unix like and to replace tab by 4 spaces.

CC