This commit adds a new configure option, --enable-race-checking
which is to be used exclusively for debugging. Also, conditionally
add tests to XFAIL_TESTS when Race Checking is enabled.
We will not maintian two different interfaces as earlier decided.
Instead, a common, single interface will be maintained. Hence, the tests
must adhere to the same format expected of the Parallel Tests.
This eliminated the use of Global Variables from the HTTPServer module
and uses the more correct threading.Threads module to spawn a new
server. However, on multi-core systems, the performance may deteriorate
when too many servers are launched due to CPython implementation of GIL.
Many artefacts from the old model still remain, sometimes as commenst,
else as executable code. These will be cleaned up soon