cperl-mode.el: Subroutine names are fontified correctly in all places

cperl-mode.el: Subroutine names are fontified correctly in all places

Subroutine names are fontified as subroutine names even if the name is also
the name of a builtin (fixing an ancient unreported bug).  Subroutine name
are just comments in comment and pod (fixing a bug introduced recently)

* lisp/progmodes/cperl-mode.el (cperl-init-faces): Move
fontification of sub declarations before that of builtins.  Don't
override existing faces when fontifying subroutine declarations.
Don't fontify method calls even if the sub names match those of
builtins.

* test/lisp/progmodes/cperl-mode-tests.el (cperl-test-fontify-sub-names):
New tests with a subroutine name in several surroundings.

* test/lisp/progmodes/cperl-mode-resources/sub-names.pl: New resource
for the new test.