Add Gmail IMAP special support.

New repository/folder classes to support "real deletion" of messages
thorugh Gmail's IMAP interface: to really delete a message in Gmail,
one has to move it to the Trash folder, rather than EXPUNGE it.

offlineimap.conf

@@ -203,7 +203,7 @@ restoreatime = no
 
 [Repository RemoteExample]
 
-# And this is the remote repository.  For now, we only support IMAP here.
+# And this is the remote repository.  We only support IMAP or Gmail here.
 
 type = IMAP
 
@@ -380,3 +380,33 @@ holdconnectionopen = no
 #
 # foldersort = lambda x, y: -cmp(x, y)
 
+
+[Repository GmailExample]
+
+# A repository using Gmail's IMAP interface.  Any configuration
+# parameter of `IMAP` type repositories can be used here.  Only
+# `remoteuser` (or `remoteusereval` ) is mandatory.  Default values
+# for other parameters are OK, and you should not need fiddle with
+# those.
+#
+# The Gmail repository will use hard-coded values for `remotehost`,
+# `remoteport`, `tunnel` and `ssl`.  (See
+# http://mail.google.com/support/bin/answer.py?answer=78799&topic=12814)
+# Any attempt to set those parameters will be silently ignored.
+#
+
+type = Gmail
+
+# Specify the Gmail user name. This is the only mandatory parameter.
+remoteuser = username@gmail.com
+
+# Deleting a message from a Gmail folder via the IMAP interface will
+# just remove that folder's label from the message: the message will
+# continue to exist in the '[Gmail]/All Mail' folder.  If `realdelete`
+# is set to `True`, then deleted messages will really be deleted
+# during `offlineimap` sync, by moving them to the '[Gmail]/Trash'
+# folder.  BEWARE: this will deleted a messages from *all folders* it
+# belongs to!
+#
+# See http://mail.google.com/support/bin/answer.py?answer=77657&topic=12815
+realdelete = no