pager: explicitly cast away strchr() constness

When we do:

  char *cp = strchr(argv[i], '=');

it implicitly removes the constness from argv[i]. We need "cp" to remain
writable (since we overwrite it with a NUL). In theory we should be able
to drop the const from argv[i], because it is a sub-pointer into our
duplicated pager_env variable.

But we get it from split_cmdline(), which uses the traditional "const
char **" type for argv. This is overly limiting, but changing it would
be awkward for all the other callers of split_cmdline().

Let's do an explicit cast with a note about why it is OK. This is enough
to silence compiler warnings about the implicit const problems.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

pager.c

@@ -108,10 +108,11 @@ const char *git_pager(struct repository *r, int stdout_is_tty)
 
 static void setup_pager_env(struct strvec *env)
 {
-	const char **argv;
+	char **argv;
 	int i;
 	char *pager_env = xstrdup(PAGER_ENV);
-	int n = split_cmdline(pager_env, &argv);
+	/* split_cmdline splits in place, so we know the result is writable */
+	int n = split_cmdline(pager_env, (const char ***)&argv);
 
 	if (n < 0)
 		die("malformed build-time PAGER_ENV: %s",