Add ability to override environment

rubygems.py

@@ -65,7 +65,7 @@ class Recipe(object):
             'PREFIX': self.options['location'],
             'RUBYLIB': os.environ.get('RUBYLIB', ''),
         }
-        return {
+        env = {
             'GEM_HOME': '%(PREFIX)s/lib/ruby/gems/1.8' % s,
             'RUBYLIB': self._join_paths(
                     '%(RUBYLIB)s',
@@ -78,6 +78,17 @@ class Recipe(object):
                     '%(PREFIX)s/bin',
                 ) % s,
         }
+        try:
+            env_override = self.options.get('environment', '')
+            env = {k: v % env
+                   for k, v in [[i.strip() for i in line.split('=', 1)]
+                                for line in env_override.split('\n')
+                                if line.strip()]
+                  }
+        except ValueError: # Unpacking impossible
+            self.log.error("Every environment line should contain a '=' sign")
+            zc.buildout.UserError('Configuration error')
+        return env
 
     def _get_latest_rubygems(self):
         if self.version: