Doesn't recognize extension-less Perl files using cperl-mode

[genehack]

When editing a Perl file that doesn't have an extension (e.g., a command script in Perl), using cperl-mode, currently dumb-jump reports Could not find rules for ’. file’..

Since cperl-mode is the most common mode for editing Perl files in Emacs, this is unfortunate. Pull request to fix this incoming in just a second tho. 8^)