We support two different ways for an IMAP prefix to be specified:
1. A text field on the IMAP configuration page. This is the most obvious to
the end user. It is also an explicit, manual configuration.
2. RFC2342 defines a NAMESPACE IMAP command to be able to query the prefix
from the IMAP server. This is an automatic configuration without any
user involvement (i.e. the UI will NOT change if a prefix is loaded in
this way)
If the user goes to the trouble of specifying a prefix, we will always honour
it instead of the namespace returned by the IMAP server -- even if the user's
configuration is wrong.
bug 1592696
Change-Id: I6b94c7aaac538f6cd9dc4694b0f1634e8c956bc1
32311cce01