Another try at making plpython autoconfiguration work correctly. Use a

Another try at making plpython autoconfiguration work correctly.  Use a
-L spec rather than assuming libpython is in the standard search path
(this returns to the way 7.4 did it).  But check the distutils output
to see if it looks like Python has built a shared library, and if so
link with that instead of the probably-not-shared library found in
configdir.