regen/HeaderParser.pm: require perl >= 5.10

This won't compile when run on earlier perls, and the reason isn't
apparent without some digging.  It turns out that it uses named capture
groups which came in 5.9.5, and the first stable release was 5.10

regen/HeaderParser.pm

@@ -1,6 +1,7 @@
 package HeaderParser;
 use strict;
 use warnings;
+use v5.10;      # Needs named capture groups
 
 # these are required below in BEGIN statements, we cant have a
 # hard dependency on them as they might not be available when