Version symbols in poppler core

This prevents crashes and collisions in the case where two poppler core libraries are in the same process.

The likely case is if an application is linked to both poppler core and a stable frontend, and poppler is updated and the application is not yet recompiled against the newer poppler core, then the newer frontend pulls in newer poppler core while the application pulls in the older poppler core and that leads to crashes. In general, this can be fixed by versioning the symbols to prevent mix and match of symbols.

Patch by Andreas Metzler ametzler@bebt.de