* ext/bitmap_allocator.h: Clean-up add/remove functions.
* src/bitmap_allocator.cc: New file. Contains the out-of-line
function definitions, static initialization of variables, and
explicit instantiations needed for the allocator.
* src/Makefile.am: Add.
* src/Makefile.in: Regenerate.
* config/linker.map.gnu: Add the necessary symbols.