Don't depend on stdbool.h for jemalloc.h

stdbool.h was only added in MSVC2013, so for MSVC2010/2012 we'd either need to export our stdbool.h, or eliminate `bool` from installed headers -- which is what I did here.

This patch will simply replace all externally-visible uses of `bool` with `int`, and cast appropriately (I believe the cast is always valid, but couldn't find confirmation or refutation of that, sadly).