Change self-description (mklink.pl is not just faster than the last

released version of mklink.sh -- the latter couldn't even handle
the ../../include/openssl case).

util/mklink.pl

 #!/usr/local/bin/perl
 
-# mklink.pl -- a faster substitute for mklink.sh.
+# mklink.pl
 
 # The first command line argument is a non-empty relative path
 # specifying the "from" directory.