debian: Don't waste time regenerating the manpage database

By default, APT regenerates the manual page database
after installing packages.   This happens for every
build and takes several seconds, so skipping it should
save quite a lot of time.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #262 from euanh/build-improvements

:relodebian: Don't waste time regenerating the manpage database