Fix for the fa_IR locale failure. The reason for the failure

Fix for the fa_IR locale failure.  The reason for the failure
was that Perl was assuming the decimal separator aka the radix
separator is one character.  The Farsi-Iranian locale crushed
that bad assumption since there the separator is 'Momayyez',
glyphwise looking somewhat like a slash, and in Unicode UTF-8
encoded in two bytes, 0xd9 0xab.

p4raw-id: //depot/perl@8625