* mu4e: don't append to attachment name when retryiing
* cosmetic
* mu4e: some updates to the reference doc
* mu4e: some cleanups
* toys/mug: remove -DGTK_DISABLE_DEPRECATED for now, since it breaks 3.10+ compilation
* mu4e: mu4e-view-fill-headers to enable/disable header filling
* mu4e: don't try to kill the visible window when there is none (thanks to thierryvolpiatto)
index: improve error message when file does not seem to be an email
* handle message-ids a bit specially, update unit tests
* mu4e: add hooks mu4e-headers-found-hook and mu4e-update-pre-hook, document them.