Allow direction commands in math mode
Use a modified webmac.tex

Based on pdfwebmac.tex, produces hyperlinked PDF.
Don’t use native_glyph() of a box!

This fixes the “sporadic shifted underbrace error” reported on the
mailing list
http://tug.org/pipermail/xetex/2013-February/024057.html
Disable synctex for now

The XeT--TeX stuff broke synctex change files, so disable it for now.
Fix segmentation fault with OT math kern

Make sure p is not null before accessing it.
Add #ifndef __cplusplus ... #endif for #define bool boolean