PRItime: introduce a new "printf format" for timestamps

Currently, Git's source code treats all timestamps as if they were
unsigned longs. Therefore, it is okay to write "%lu" when printing them.

There is a substantial problem with that, though: at least on Windows,
time_t is *larger* than unsigned long, and hence we will want to switch
away from the ill-specified `unsigned long` data type.

So let's introduce the pseudo format "PRItime" (currently simply being
defined to "lu") to make it easier to change the data type used for
timestamps.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/vcs-svn/fast_export.c b/vcs-svn/fast_export.c
index 97cba39..6c9f286 100644
--- a/vcs-svn/fast_export.c
+++ b/vcs-svn/fast_export.c
@@ -73,7 +73,7 @@ void fast_export_begin_note(uint32_t revision, const char *author,
 	static int firstnote = 1;
 	size_t loglen = strlen(log);
 	printf("commit %s\n", note_ref);
-	printf("committer %s <%s@%s> %lu +0000\n", author, author, "local", timestamp);
+	printf("committer %s <%s@%s> %"PRItime" +0000\n", author, author, "local", timestamp);
 	printf("data %"PRIuMAX"\n", (uintmax_t)loglen);
 	fwrite(log, loglen, 1, stdout);
 	if (firstnote) {
@@ -107,7 +107,7 @@ void fast_export_begin_commit(uint32_t revision, const char *author,
 	}
 	printf("commit %s\n", local_ref);
 	printf("mark :%"PRIu32"\n", revision);
-	printf("committer %s <%s@%s> %lu +0000\n",
+	printf("committer %s <%s@%s> %"PRItime" +0000\n",
 		   *author ? author : "nobody",
 		   *author ? author : "nobody",
 		   *uuid ? uuid : "local", timestamp);