postgresql 9.3.0

- Use sha256 instead of sha1, because the upstream download site
  provides the former.

- Remove various workarounds for PL/Python build issues.  These have all
  been fixed upstream.

- Remove caveat about shared memory configuration, which is no longer
  applicable.

Closes #22411.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>