mail/fetchmail: update to 6.4.31.

Since the distro was built with a newer autoconf, the patch-configure
no longer applies and has been converted to a post-patch REINPLACE_CMD,
also to avoid future breakage.

This also adds one upstream Git patch to fix the version and date tags
in the manual page.

PR: 265251
Approved by: Corey Halpin (maintainer)