Add decodefoldernames option to decode IMAP folder names using UTF-7.

Signed-off-by: Tommie Gannert <tommie@gannert.se>

offlineimap.conf

@@ -762,6 +762,20 @@ remoteuser = username
 #reference = Mail
 
 
+# This option stands in the [Repository RemoteExample] section.
+#
+# IMAP defines an encoding for non-ASCII ("international") characters. Enable
+# this option if you want to decode them to the nowadays ubiquitous UTF-8.
+#
+# Note that the IMAP 4rev1 specification (RFC 3501) allows both UTF-8 and
+# modified UTF-7 folder names.
+#
+# This option is disabled by default to retain compatibility with older versions
+# of offlineimap.
+#
+#decodefoldernames = no
+
+
 # This option stands in the [Repository RemoteExample] section.
 #
 # In between synchronisations, OfflineIMAP can monitor mailboxes for new