"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>

cache.h

@@ -382,6 +382,7 @@ extern int receive_keep_pack(int fd[2], const char *me, int quiet, int);
 
 /* pager.c */
 extern void setup_pager(void);
+extern int pager_in_use;
 
 /* base85 */
 int decode_85(char *dst, char *line, int linelen);

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;

git.c

@@ -251,6 +251,11 @@ int main(int argc, const char **argv, char **envp)
 		cmd = *++argv;
 		argc--;
 
+		if (!strcmp(cmd, "-p") || !strcmp(cmd, "--paginate")) {
+			setup_pager();
+			continue;
+		}
+
 		if (strncmp(cmd, "--", 2))
 			break;
 

pager.c

@@ -5,6 +5,8 @@
  * something different on Windows, for example.
  */
 
+int pager_in_use;
+
 static void run_pager(const char *pager)
 {
 	execlp(pager, pager, NULL);
@@ -24,6 +26,8 @@ void setup_pager(void)
 	else if (!*pager || !strcmp(pager, "cat"))
 		return;
 
+	pager_in_use = 1; /* means we are emitting to terminal */
+
 	if (pipe(fd) < 0)
 		return;
 	pid = fork();