Added option to test for allocatable memory.

Patch by Eric B Munson <emunson@akamai.com>
Prepare for release.
Fixed typo
Started updated Debian files.
Correct man page to display what we really do.
Fix code and docs to corectly use and describe <interval>.
Fix module handling for wd-keepalive as well.
Cleaning up init files a bit.
Added systemd service files.
Correctly convert variable, otherwise we might get an overflow.
Make sure /etc/init.d/sendsigs does not kill wd_keepalive.
Remove default file for Debian again. It should have never been re-added
because it is auto-generated.
Updated systemd.service files.
Updated Debian version.