msvc: Fix some "expr evaluates to function" compiler warnings

In particular, the following warning is issued while compiling
notes.c:

    notes.c(927) : warning C4550: expression evaluates to a \
function which is missing an argument list

along with identical warnings on lines 928, 1016 and 1017.

In order to suppress the warning, we change the definition of
combine_notes_fn, so that the symbol type is an (explicit)
"pointer to function ...".  As a result, several other
declarations need some minor fix-up to take account of the
new typedef.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin.h

@@ -26,13 +26,13 @@ struct notes_rewrite_cfg {
 	struct notes_tree **trees;
 	const char *cmd;
 	int enabled;
-	combine_notes_fn *combine;
+	combine_notes_fn combine;
 	struct string_list *refs;
 	int refs_from_env;
 	int mode_from_env;
 };
 
-combine_notes_fn *parse_combine_notes_fn(const char *v);
+combine_notes_fn parse_combine_notes_fn(const char *v);
 struct notes_rewrite_cfg *init_copy_notes_for_rewrite(const char *cmd);
 int copy_note_for_rewrite(struct notes_rewrite_cfg *c,
 			  const unsigned char *from_obj, const unsigned char *to_obj);

builtin/notes.c

@@ -313,7 +313,7 @@ int commit_notes(struct notes_tree *t, const char *msg)
 	return 0;
 }
 
-combine_notes_fn *parse_combine_notes_fn(const char *v)
+combine_notes_fn parse_combine_notes_fn(const char *v)
 {
 	if (!strcasecmp(v, "overwrite"))
 		return combine_notes_overwrite;

notes.h

@@ -18,7 +18,7 @@
  * combine_notes_concatenate(), which appends the contents of the new note to
  * the contents of the existing note.
  */
-typedef int combine_notes_fn(unsigned char *cur_sha1, const unsigned char *new_sha1);
+typedef int (*combine_notes_fn)(unsigned char *cur_sha1, const unsigned char *new_sha1);
 
 /* Common notes combinators */
 int combine_notes_concatenate(unsigned char *cur_sha1, const unsigned char *new_sha1);
@@ -38,7 +38,7 @@ extern struct notes_tree {
 	struct int_node *root;
 	struct non_note *first_non_note, *prev_non_note;
 	char *ref;
-	combine_notes_fn *combine_notes;
+	combine_notes_fn combine_notes;
 	int initialized;
 	int dirty;
 } default_notes_tree;