hscript integration for conditionals + postBuild command

Hi,
I have talked a bit about theses features by mail a long time ago, and here they are.

THe thing is that we had some issues with current conditionals expressions.  using hscript helps a lot BUT breaks the XML standard compatibility with && operator.
For us, having a robust compilation is the most important thing.

There's also the postbuild command feature, which is really important to have in the build system.
Cheers
Thomas