Make the second menu entry an action instead of a report

"Apply now" had nothing to do in the normal case. Enabling applies, the
watcher handles everything installed afterwards, and the settings and
applications screens apply on their way out - so pressing it answered
"already applied to 14 applications" and that was the whole interaction.

It is now "Re-apply everything": the state is taken back and written again
from scratch. That is the answer to the question the status block can raise
but nothing could act on - Steam showing as not patched after a client
update, an application that drifted, a flag file edited by hand.

Uninstalling an application used to leave the entry shadowing it behind, in
the user home where the package manager cannot see it, offering to start a
program that is gone. A plain apply only looks at what exists now, so the
watcher never noticed either. Those are removed on every apply now, not just
when rebuilding.

doc/middleclick-autoscroll.1.scd

@@ -36,10 +36,17 @@ is refused.
 *disable*
 	Turn it off and put every file that was changed back the way it was.
 
-*apply*
+*apply* [*--rebuild*]
 	Apply to anything that has appeared since the last run. This is what the
 	watcher calls; running it by hand is only needed when the watcher is off.
 
+	Entries left behind by an application that has since been uninstalled are
+	removed here too - the entry shadowing it lives in the user's home, where
+	the package manager that removed the application cannot see it.
+
+	With *--rebuild* everything is taken back first and written again from
+	scratch. That is the repair: it does not care what looks correct already.
+
 *status*
 	How many applications are covered, whether Steam is patched, and when the
 	last run was.