Cleanup systemd files

- Added documentation lines for each service
- Added Restart on-failure for each service
- Remove Alias from -dir (only for .target unit)
- Added soft dependency for postgresql & mysql for bareos-dir in
  After= line so systemd know we prefer to start once the db is up

Fixes #240: Improve systemd service files
Fix problem with poll() on AIX.

Its seems that unlike Linux, Solaris and Windows AIX has a somewhat
other idea in what flags it needs in the events field of the poll
structure. This patch makes poll() work on AIX and should also keep it
working on the other platforms.
Fix AIX configure output.

It seems AIX compiles with large file support but the configure summary
doesn't show that. As this may triggers others to take the wrong
conclusion set largefile_support explictly to yes just like is done for
BSDI and FreeBSD.
Make read/written NDMP bytes 64 bits.

A 32 bit counter will wrap around when storing the size of an NDMP save
or restore so use a 64 bits value.
Merge branch 'master' of https://github.com/bareos/bareos