Renamed ExtensionManager to BuildPackManager.  Moved from builder to installer.
Added ExtensionInstaller and associated tests.  This allows the inclusion of extension or plugin modules in a build pack.
Removed chdir call.  Not strictly needed since git will clone to the specified directory.  Also broken several tests.
Fixed up some unit tests.  Mostly due to test data changes.
Switched download to increase speed of test.
Renamed TEMP_DIR to TMPDIR. Added all environment variables to the context.
Added standard output logging method.