Make unresolvable link destinations warnings instead of errors.

See bug 693314 (file Z23-04.pdf) for an example file.
Fix 694952: Limit Type 3 font glyph bbox size.

Don't let a glyph's bbox be too much bigger than the font bbox.
Add an application agnostic memory handler for libjpeg

This adds a custom memory management layer between libjpeg and the calling
app - in such a way that the code can be shared between mupdf and
Ghostscript/PDL.
Remove jmorecfg.h from includes.