log -L: :pattern:file syntax to find by funcname

This new syntax finds a funcname matching /pattern/, and then takes from there
up to (but not including) the next funcname.  So you can say

  git log -L:main:main.c

and it will dig up the main() function and show its line-log, provided
there are no other funcnames matching 'main'.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

line-range.h

@@ -19,7 +19,8 @@ typedef const char *(*nth_line_fn_t)(void *data, long lno);
 extern int parse_range_arg(const char *arg,
 			   nth_line_fn_t nth_line_cb,
 			   void *cb_data, long lines,
-			   long *begin, long *end);
+			   long *begin, long *end,
+			   const char *path);
 
 /*
  * Scan past a range argument that could be parsed by