"git -p cmd" to page anywhere

This allows you to say:

	git -p diff v2.6.16-rc5..

and the command pipes the output of any git command to your pager.

[jc: this resurrects a month old RFC patch with improvement
 suggested by Linus to call it --paginate instead of --less.]

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -112,7 +112,7 @@ int git_diff_config(const char *var, const char *value)
 			diff_use_color_default = 1; /* bool */
 		else if (!strcasecmp(value, "auto")) {
 			diff_use_color_default = 0;
-			if (isatty(1)) {
+			if (isatty(1) || pager_in_use) {
 				char *term = getenv("TERM");
 				if (term && strcmp(term, "dumb"))
 					diff_use_color_default = 1;