python added to systemtap.apps testsuite

[Stan Cox]

The systemtap testsuite has a systemtap.apps subpackage where some 
packages with sdt markers are built and the markers are tested.   python 
doesn't (yet) have upstream sdt marker support.  However, it has been 
added to the testsuite by downloading and  patching the upstream  python 
sources.  python2.stp and python3.stp provide support for backtracing 
the python stack and fetching python variables.  If the test is run via:
  RUNTESTFLAGS="-v python.exp" make installcheck
then the test is not cleaned up so it is possible to inspect how python 
is supported by the testsuite.