Fix build error in msgs-count.scm

mu:run-stats expects the passed-in function to take 3 arguments. The
third argument applies to gnuplot only, which is not applicable to the
count function in msgs-count.scm.
Merge pull request #534 from che2/fix-msgs-count

guile: Fix build error in msgs-count.scm
Add a missing keybinding to doc for previous query
Merge pull request #535 from xuhdev/patch-1

mu4e: Add a missing keybinding to doc for previous query
mu4e: mu4e-headers-find-if-next: move before search

when searching for the next match, go the end of the current line; when
searching for the previous match, go to the beginning of the current
line.
mu4e: org: allow customization of linking in headers mode

Depending on org-mu4e-link-query-in-headers-mode, we can link to the
query or the particular message.
mu4e: mu4e~view-compose-contact takes full address when available