Fix recent accidental omission in pg_proc.dat

Fix recent accidental omission in pg_proc.dat

ed1a88dda added support functions for the ntile(), percent_rank() and
cume_dist() window functions but neglected to actually add these support
functions to the pg_proc entry for the corresponding window function.

Also, take this opportunity to add these window functions to one of the
regression tests added in ed1a88dda to give the support functions a little
bit of exercise.  If I'd done that in the first place then the omission
would have been more obvious.

Bump the catversion, again.