Added limits for mongodb upstart.

At this time, you can't. limits.conf(5) is the configuration for pam_limits(8), which is activated by the PAM stack according to the configuration in /etc/pam.d. However, start-stop-daemon(8) as launched from an init.d script doesn't pass through the PAM stack, so those kinds of settings are never applied.

Debian bug #302079 contains a patch to enable setting limits from start-stop-daemon(8), but the bug has been open since 2005 and the patch hasn't been merged yet.