MFC r262810, r262862, r264105, r264107:

r262810:
  Merge enabling building FreeBSD/arm images as part of the
  release build process.

r262862:
  Provide backwards-compatibility with release.conf SVNROOT
  entries that do not have a trailing '/'.

r264105:
  Add ZEDBOARD support for release builds.

r264107:
  Remove only-works-on-amd64 restriction.

* Local modifications to stable/9:
  - Set SRCBRANCH from head/ to stable/9/.

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