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>

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.

This patch adds search behaviour to allow searching in the body of the
messages, the entire text (body + header), and searching just the from
header.

Signed-off-by: Wagner Riffel <wgrriffel@gmail.com>

This fixes ~sircmpwn/aerc2#245. This sets up the imap client to send
error messages to the logger of the worker. Errors now end up in the
bottom status line.

https://todo.sr.ht/~sircmpwn/aerc2/245

This allows backends which can't always be compiled due to missing
dependencies (say libnotmuch) to be compiled conditionally with buildflags.

    imaps+oauthbearer://user:token@host?token_endpoint=...

 - the config Source password is used as access token if
   no token_endpoint parameter is set
 - the config Source password is used as refresh token if
   token_endpoint parameter is set, and used to exchange
   with an access token

The implementation has only been tested with Gmail.

    source = imaps+oauthbearer://{username}:{refersh_token}@imap.gmail.com:993? \
    client_id=XX&\
    client_secret=XX&\
    token_endpoint=https%3A%2F%2Faccounts.google.com%2Fo%2Foauth2%2Ftoken

client credentials created with

    https://console.developers.google.com/apis/credentials

refresh token created with

    https://github.com/google/gmail-oauth2-tools/blob/master/python/oauth2.py

rel: https://todo.sr.ht/~sircmpwn/aerc2/42