git-log produces no output

When $PAGER is set to 'less -i', we used to fail because we
assumed the $PAGER is a command and simply exec'ed it.

Try exec first, and then run it through shell if it fails.  This
allows even funkier PAGERs like these ;-):

	PAGER='sed -e "s/^/`date`: /" | more'
	PAGER='contrib/colordiff.perl | less -RS'

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

pager.c

@@ -8,6 +8,7 @@
 static void run_pager(const char *pager)
 {
 	execlp(pager, pager, NULL);
+	execl("/bin/sh", "sh", "-c", pager, NULL);
 }
 
 void setup_pager(void)
@@ -47,5 +48,6 @@ void setup_pager(void)
 
 	setenv("LESS", "-S", 0);
 	run_pager(pager);
+	die("unable to execute pager '%s'", pager);
 	exit(255);
 }