Ports using USE_PYTHON=distutils are now flavored.  They will
  automatically get flavors (py27, py34, py35, py36) depending on what
  versions they support.

  There is also a USE_PYTHON=flavors for ports that do not use distutils
  but need FLAVORS to be set.  A USE_PYTHON=noflavors can be set if
  using distutils but flavors are not wanted.

  A new USE_PYTHON=optsuffix that will add PYTHON_PKGNAMESUFFIX has been
  added to cope with Python ports that did not have the Python
  PKGNAMEPREFIX but are flavored.

  USES=python now also exports a PY_FLAVOR variable that contains the
  current python flavor.  It can be used in dependency lines when the
  port itself is not python flavored.  For example, deskutils/calibre.

  By default, all the flavors are generated.  To only generate flavors
  for the versions in PYTHON2_DEFAULT and PYTHON3_DEFAULT, define
  BUILD_DEFAULT_PYTHON_FLAVORS in your make.conf.

  In all the ports with Python dependencies, the *_DEPENDS entries MUST
  end with the flavor so that the framework knows which to build/use.
  This is done by appending '@${PY_FLAVOR}' after the origin (or
  @${FLAVOR} if in a Python module with Python flavors, as the content
  will be the same).  For example:

    RUN_DEPENDS= ${PYTHON_PKGNAMEPREFIX}six>0:devel/py-six@${PY_FLAVOR}

PR:		223071
Reviewed by:	portmgr, python
Sponsored by:	Absolight
Differential Revision:	https://reviews.freebsd.org/D12464

PR:		213743
Submitted by:	mat
Exp-run by:	antoine
Sponsored by:	Absolight

- 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

With hat:	python@

minor COMMENT typos and surrounding whitespace fixes. A few Makefiles
where not included as they contain Latin-1 characters that break
the Phabricator workflow. Category W.

CR:		D510
Approved by:	portmgr (bapt)

- Stage support
- Bump PORTREVISION