Fixed silent keyword arg to config.from_envvar.

The ``silent`` keyword argument to Config.from_envvar was not being honored
if the environment variable existed but the file that it mentioned did not.
The fix was simple - pass the keyword argument on to the underlying call to
``from_pyfile``.  I also noticed that the return value from ``from_pyfile``
was not being passed back so I fixed that as well.

flask/config.py

@@ -106,8 +106,7 @@ class Config(dict):
                                'loaded.  Set this variable and make it '
                                'point to a configuration file' %
                                variable_name)
-        self.from_pyfile(rv)
-        return True
+        return self.from_pyfile(rv, silent=silent)
 
     def from_pyfile(self, filename, silent=False):
         """Updates the values in the config from a Python file.  This function

flask/testsuite/config.py

@@ -69,6 +69,24 @@ class ConfigTestCase(FlaskTestCase):
         finally:
             os.environ = env
 
+    def test_config_from_envvar_missing(self):
+        env = os.environ
+        try:
+            os.environ = {'FOO_SETTINGS': 'missing.cfg'}
+            try:
+                app = flask.Flask(__name__)
+                app.config.from_envvar('FOO_SETTINGS')
+            except IOError, e:
+                msg = str(e)
+                self.assert_(msg.startswith('[Errno 2] Unable to load configuration '
+                                            'file (No such file or directory):'))
+                self.assert_(msg.endswith("missing.cfg'"))
+            else:
+                self.assert_(0, 'expected config')
+            self.assert_(not app.config.from_envvar('FOO_SETTINGS', silent=True))
+        finally:
+            os.environ = env
+
     def test_config_missing(self):
         app = flask.Flask(__name__)
         try: