[release,automake] Stop overriding docdir needlessly.

docdir is variable of automake and its by default set to $(datadir)/doc/dune-common.
Therefore there is not need to set it here.
(cherry picked from commit 7655d4f66357c8bbe4f71e3ddea7d27e58916f44)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[release,cmake] Install manpage of dunecontrol.
(cherry picked from commit a897d8f97fce527c7aa28895978ec600473c763b)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[release,cmake] Fixes installation directory of DoxyFile.
(cherry picked from commit d5adf804b75c5251af23692194bea3f6357e6dd9)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>