merge-pod: Be more compatible with older perl

merge-pod: Be more compatible with older perl

merge-pod works fine with perl 5.00503, if we eliminate the 3-argument
invocation of open(). So, replace the open() calls with their
2-argument equivalent, and relax the version requirement a bit.

Reviewed-on: http://gerrit.openafs.org/3661
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 2045653647fc2de451c9615f18316416de7e1657)

Change-Id: Ie3945eb37628ed3bd55f9cb53dd2f4d122f3b087
Reviewed-on: http://gerrit.openafs.org/3778
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>