Append _pullx_ and _pullf to pull files when -deffnm used.

Append _pullx_ and _pullf to pull files when -deffnm used.

Changes -deffnm behavior for pulling so that the pullx and pullf
files don't collide. Previously, this resulted in one being
backed up and checkpoint restarts failing when -deffnm was used.
(Technically this applies to anything where -px and -pf are identical
 and not explicitly set, but that only happens with -deffnm.)

Additionally return fatal error if -px or -pf set and output files
collide.

Fix is now localized to the pull code.

Fixes #942 except for log file collision with pull-rotation.

Change-Id: I27b8b4ced0f307905e2c2ea4fb260376dd25dc32