Merge branch 'ew/find-perl-on-freebsd-in-local' into maint

Recent FreeBSD stopped making perl available at /usr/bin/perl;
switch the default the built-in path to /usr/local/bin/perl on not
too ancient FreeBSD releases.

* ew/find-perl-on-freebsd-in-local:
config.mak.uname: correct perl path on FreeBSD