mail: actually use the verifycert config value

The mail module only verifies the smtp ssl certificate if 'verifycert' is enabled
(the default). The 'verifycert' can take three possible values:

- 'strict'
- 'loose'
- any "False" value, eg: 'false' or '0'

We tested the validity of the third value, but never converted it to actual
falseness, making 'False' an equivalent for 'loose'.

This changeset fixes it.

mercurial/mail.py

@@ -104,6 +104,7 b' def _smtp(ui):'
         if util.parsebool(verifycert) is not False:
             raise util.Abort(_('invalid smtp.verifycert configuration: %s')
                              % (verifycert))
+        verifycert = False
     if (starttls or smtps) and verifycert:
         sslkwargs = sslutil.sslkwargs(ui, mailhost)
     else: