Teach git var about GIT_PAGER

Expose the command found by setup_pager() for scripts to use.
Scripts can use this to avoid repeating the logic to look for a
proper pager in each command.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/var.c b/var.c
index b502487..d9892f8 100644
--- a/var.c
+++ b/var.c
@@ -18,6 +18,15 @@
 	return pgm;
 }
 
+static const char *pager(int flag)
+{
+	const char *pgm = git_pager();
+
+	if (!pgm)
+		pgm = "cat";
+	return pgm;
+}
+
 struct git_var {
 	const char *name;
 	const char *(*read)(int);
@@ -26,6 +35,7 @@
 	{ "GIT_COMMITTER_IDENT", git_committer_info },
 	{ "GIT_AUTHOR_IDENT",   git_author_info },
 	{ "GIT_EDITOR", editor },
+	{ "GIT_PAGER", pager },
 	{ "", NULL },
 };