syncdomain: use flock, not file existence

There were cases when syncdomain was terminated abnormally, keeping the
lock file existing. After that the syncdomain was not able to resume
until the lockfile was deleted.

This patch uses flock(), adds ability to disable locking logic
(--nolock), and to print significant errors to the STDERR (--stderr) to inform
sysadmin using mail.
shortenIfName: don't lowercase "AC-in" port
SNMP support for Cisco 2960X-24PS-L, 2960X-24PD-L
Merge branch 'syncdomain'