Folder: Implement __eq__ for folders

This allows to compare folders directly with strings. It also allows
constructs such as "if 'moo' in repo.getfolders()".

See the code documentation for the exact behavior (it basically is equal if
it's the same instance *or* a string matching the untranslated folder name.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/folder/Base.py

@@ -479,3 +479,20 @@ class BaseFolder(object):
                 self.ui.error(e, exc_info()[2], "Syncing folder %s [acc: %s]" %\
                                   (self, self.accountname))
                 raise # raise unknown Exceptions so we can fix them
+
+    def __eq__(self, other):
+        """Comparisons work either on string comparing folder names or
+        on the same instance
+
+        MailDirFolder('foo') == 'foo' --> True
+        a = MailDirFolder('foo'); a == b --> True
+        MailDirFolder('foo') == 'moo' --> False
+        MailDirFolder('foo') == IMAPFolder('foo') --> False
+        MailDirFolder('foo') == MaildirFolder('foo') --> False
+        """
+        if isinstance(other, basestring):
+            return other == self.name
+        return id(self) == id(other)
+
+    def __ne__(self, other):
+        return not self.__eq__(other)