Support for --with-pydebug builds.
python.jam:
Support for the specification of "_d" extension suffix.
In compute-default-paths, fixed the check for residence in
a "PCBuild.*" directory so we can build against Windows Python built
in a source distribution.
common.jam:
Fixed generation of the "y" tag to look for <python-debugging>on
rather than the whole debug-python build variant.
Fixed some grammar and spelling.
virtual-target.jam:
Added the ability to forego the prepending of "." to a
generated-target-suffix by specifying the suffix enclosed in <...>
libs/python/build/Jamfile.v2:
#define BOOST_DEBUG_PYTHON when <python-debugging>on