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>

t/t4018-diff-funcname.sh

@@ -32,7 +32,7 @@ EOF
 
 sed 's/beer\\/beer,\\/' < Beer.java > Beer-correct.java
 
-builtin_patterns="bibtex cpp csharp fortran html java objc pascal php python ruby tex"
+builtin_patterns="bibtex cpp csharp fortran html java objc pascal perl php python ruby tex"
 for p in $builtin_patterns
 do
 	test_expect_success "builtin $p pattern compiles" '