Merge branch 'km/imap-send-libcurl-options'

Now imap-send learned to talk to the server using cURL library,
allow the same GIT_CURL_VERBOSE environment variable to control the
verbosity of the chattering.

* km/imap-send-libcurl-options:
  imap-send.c: set CURLOPT_USE_SSL to CURLUSESSL_TRY
  imap-send.c: support GIT_CURL_VERBOSE