change manisort to produce a more intuitive order

change manisort to produce a more intuitive order

Dictionary sort order on filenames is very counter-intuitive, and
produces surprising sort orders.

What this patch does is sort things so that the following should
always be true:

1. Case insensitive textual order
   Eg: Foo and foo and FOO should sort together in ascibetical order

2. Shorter dirs go before longer dirs with a common prefix
   Eg: lib/Foo/ should go before lib/Foo-Thing/

3. Base filename goes before dir of the same name
   Eg: lib/Foo.pm should sort before lib/Foo/Bar.pm

This also refactors the MANIFEST sort code in Porting/manisort and
Porting/pod_rules.pm files into Porting/pod_lib.pl