When deleting a message, sometimes FetchDirectoryContents will fire.
FetchDirectoryContents will return a smaller set of UIDs since messages
have been deleted. This operation races with fetching from the seqMap in
client.ExpungeUpdate. Only recreate the seqMap if it can grow so that
messages will continue to be expunged.

Signed-off-by: Kevin Kuehler <keur@xcf.berkeley.edu>

Right now notmuch panics if something goes wrong in the configure event.
This patch checks for that and returns an error instead, so that we can at least
get the UI up and running (and all the other accounts)

The experience will be completely degraded until another configure event occurs.

A segmentation fault occurs when using the notmuch backend and a `query-map`
file that contains blank lines or comments.

Configure an oauthbearer source without a token_endpoint
parameter would panic due to nil pointer dereference

  Example
    source=imaps+oauthbearer://frode.aa%40gmail.com@imap.gmail.com:993
    source-cred-cmd=pass oatuh2 frode.aa@gmail.com

token_endpoint is not required as it will use the provided
password as access_token when it is not set

This changes the search flags for maildir and imap backends.

They now no longer use -t for searching all text. This seems to make
more sense as being the targeted recipient. I have similarly added Cc
for -c. The text search now resides under -a for all text.

There is a command and config option. The criteria are a list of the
sort criterion and each can be individually reversed.

This only includes support for sorting in the maildir backend currently.
The other backends are not supported in this patch.

This populates the directory info model properly when requested,
allowing the fields to be relied upon elsewhere.

This also sends the dirinfo when new messages come in.

Basic searching is supported with the following:
- read messages
- unread messages
- from addresses
- text in body
- text in subject
- text in all

The implementation loops through all messages in the selected directory.
It tries to be smart by detecting which parts of each message the search
query needs to use and only loads these from the filesystem.