Revert "Increase the PW_BUF_SIZE so the getgrnam_r() can process large user"

This reverts commit 2fa28eb68df3799bf3ad7dd000a12665ad4b5467.

Conflicts:

	NEWS
Don't allow PMI_TIME to be zero which will cause floating exception.
Format alignment
Fix purging of old reservation errors in database.
Merge remote-tracking branch 'origin/slurm-2.6'