refactor rez_release.release_from_path into a class that will become the base class of specialized release procedures (e.g. svn, git, hg, etc)
rez_release: factor out a SvnRezRelease from the base RezRelease class
rez_release: create a working svn-free release mode.  provide a way to register new release modes.  avoid use of subprocess where built-in python functions will work.
rez_release: fix a few bugs related to the switch to python directory functions
rez_release: add RezRelease.available() and list_available_release_modes() for determining which modes are applicable to a give directory/setup.  This makes 'base' mode the default when pysvn cannot be imported.
rez_release: use copytree with hard links instead of a symbolic link to the directory
rez release: check for valid svn directory when testing if svn release mode is available
Refactor RezRelease base class so that init now only takes a path, and move other other arguments to RezRelease.release().
Add RezReleaseUnsupportedMode.
Rename RezRelease to RezReleaseMode
Refactor SvnRezRelease so that it serves as a better model for implementing new release modes.
rez-release help: Replace references to 'SVN' with more generic 'VCS'.
Change rez-svn-print-last-tag to use methods on rez_release.SvnRezReleaseMode
Add a mercurial release mode.
Add a cached property for the last_tagged_revision.  Provide get_changelog() method for Mercurial.
Mac port of rez + tweak to init.csh file.

Cover issues #27, #26, #25, #24, #23.
Fix https://github.com/nerdvegas/rez/issues/29
Allow Darwin to pretty print error in the console
The examples/demo runs fully on the Mac !

A good step towarad #24
rez is taken on osx so change to use rez- variants

cf #30
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Fix typo in configure.sh ...