diff: funcname and word patterns for perl

The default function name discovery already works quite well for Perl
code... with the exception of here-documents (or rather their ending).

 sub foo {
	print <<END
 here-document
 END
	return 1;
 }

The default funcname pattern treats the unindented END line as a
function declaration and puts it in the @@ line of diff and "grep
--show-function" output.

With a little knowledge of perl syntax, we can do better.  You can
try it out by adding "*.perl diff=perl" to the gitattributes file.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -494,6 +494,8 @@ patterns are available:
 
 - `pascal` suitable for source code in the Pascal/Delphi language.
 
+- `perl` suitable for source code in the Perl language.
+
 - `php` suitable for source code in the PHP language.
 
 - `python` suitable for source code in the Python language.