MFC r283573, r283574, r283575, r283576, r283580, r283593, r283618:

MFC r283573, r283574, r283575, r283576, r283580, r283593, r283618:

 r283573:
  Remove a continuation on error, since the relevant behavior can
  only occur if a particular file exists.

 r283574:
  Set STAGE_TARGETS only if RELEASEDIR exists.

 r283575:
  Remove duplicate exists() sanity check.

 r283576:
  Reindent after previous commit.

 r283580:
  Use SVNREVISION and BUILDDATE if passed into the make(1)
  environment, fallback to trying to figure it out otherwise.

 r283593:
  Fix a typo in a comment.

 r283618:
  Invert the build date and svn revision to match the namimg
  convention that has been in use for a while.

Sponsored by:	The FreeBSD Foundation

git-svn-id: svn://svn.freebsd.org/base/stable/10@283672 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f