Increase possible delay for reservation time

Increase the range of possible reservation time values to allow
for a really long RPC delay (possibly due to slurmctld fail over
from primary to backup controller).
Also change to a #define value for clarity
bug 527
license reconfig bug

This fixes a problem where a job contains a license that is removed
in a slurmctld reconfiguration. Without this change, the job would
be left with a non-zero license_list pointer referencing memory that
had been freed
bug 527
Change code to use macro

No change in underlying logic
Merge branch 'slurm-2.6'