userdiff/perl: anchor "sub" and "package" patterns on the left

The userdiff funcname mechanism has no concept of nested scopes ---
instead, "git diff" and "git grep --show-function" simply label the
diff header with the most recent matching line.  Unfortunately that
means text following a subroutine in a POD section:

	=head1 DESCRIPTION

	You might use this facility like so:

		sub example {
			foo;
		}

	Now, having said that, let's say more about the facility.
	Blah blah blah ... etc etc.

gets the subroutine name instead of the POD header in its diff/grep
funcname header, making it harder to get oriented when reading a
diff without enough context.

The fix is simple: anchor the funcname syntax to the left margin so
nested subroutines and packages like this won't get picked up.  (The
builtin C++ funcname pattern already does the same thing.)  This means
the userdiff driver will misparse the idiom

	{
		my $static;
		sub foo {
			... use $static ...
		}
	}

but I think that's worth it; we can revisit this later if the userdiff
mechanism learns to keep track of the beginning and end of nested
scopes.

Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

userdiff.c

@@ -60,8 +60,8 @@ PATTERNS("pascal",
 	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
 	 "|<>|<=|>=|:=|\\.\\."),
 PATTERNS("perl",
-	 "^[ \t]*package .*;\n"
-	 "^[ \t]*sub .* \\{\n"
+	 "^package .*;\n"
+	 "^sub .* \\{\n"
 	 "^[A-Z]+ \\{\n"	/* BEGIN, END, ... */
 	 "^=head[0-9] ",	/* POD */
 	 /* -- */