ENH : checkout current HEAD in git_rev not given

If the git_url is local and a git_rev is not given, then assume
that we want to build off of the current HEAD
BUG : fix  git-related envs being blow away

Update the globals with more specific envs later.
Merge pull request #238 from tacaswell/git_head

Git head
Add test_metadata.py, which should have been added a long time ago
Merge branch 'master' of github.com:conda/conda-build
add error if they try to mix their packages into Anaconda channel
update changelog
Ensure proper cache name (fixes #245)

This was causing issues on Windows via binstar-build because
binstar-build removes the remotes (prevents sniffing of any
authorization tokens in the remote).
Merge pull request #249 from conda/fix/local-git-without-remote

Ensure proper cache name (fixes #245)
Update CHANGELOG
Warn if the installed version of conda-build is out of date
Update CHANGELOG
add release date
Handle symlinks in built packages

Symlinks to paths outside conda-bld are fine. Symlinks to paths in the build
prefix are fine, but they must be relative. The post script now makes these
symlinks relative if they are absolute. Symlinks to paths in conda-bld outside
the build prefix (such as the source directory) are disallowed and give an
error.

Fixes #97.
Merge branch 'master' of github.com:conda/conda-build
Update CHANGELOG