Added last_mod_time parameter to setfsize*, replaceseg, replacetapecopy and setsegattr. Also checked for potential concurrent modifications of the files in these procedures, based on the last_mod_time and prevent the changes to take place when needed

so it can be 32x4 - 128bit checksum (MD5) maximum for the moment

Before this modification, the _net_isclosed() function called poll() with a minimum timeout of 10 milliseconds.  The generation of showqueues data indirectly calls _net_isclosed() two times per listed drive or request.  This means showqueues could not display more than 50 drives or requests per second.  The VDQM has been known to queue 2000 requests during production, this would mean a 40 second wait for the user and of one of the VDQM threads tied up for the same period.  This modification has set the poll() timeout to 0.

and better phrasing of recall related errors

and better phrasing of recall related errors