- Replace ${MASTER_SITE_FOO} with FOO.
- Merge MASTER_SITE_SUBDIR into MASTER_SITES when possible. (This means 99.9%
  of the time.)
- Remove occurrences of MASTER_SITE_LOCAL when no subdirectory was present and
  no hint of what it should be was present.
- Fix some logic.
- And generally, make things more simple and easy to understand.

While there, add magic values to the FESTIVAL, GENTOO, GIMP, GNUPG, QT and
SAMBA macros.

Also, replace some EXTRACT_SUFX occurences with USES=tar:*.

Checked by:	make fetch-urlall-list
With hat:	portmgr
Sponsored by:	Absolight