Win32 regression fixes:

. only use the -W flag on pwd for $pkglibdir. All the other paths need
to be seen as MSys type paths, whereas $pkglibdir needs to be expressed
as a genuine windows path.
. run single tests in the background and explicitly wait for them -
solves the problem of the MSys shell not waiting properly for the copy
test to finish.
. use pg_ctl to shut down the test postmaster - no more use of ad hoc
kill programs or the task manager.

Andrew Dunstan