strvec: rename struct fields

The "argc" and "argv" names made sense when the struct was argv_array,
but now they're just confusing. Let's rename them to "nr" (which we use
for counts elsewhere) and "v" (which is rather terse, but reads well
when combined with typical variable names like "args.v").

Note that we have to update all of the callers immediately. Playing
tricks with the preprocessor is hard here, because we wouldn't want to
rewrite unrelated tokens.

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

environment.c

@@ -164,7 +164,7 @@ static const char *getenv_safe(struct strvec *argv, const char *name)
 		return NULL;
 
 	strvec_push(argv, value);
-	return argv->argv[argv->argc - 1];
+	return argv->v[argv->nr - 1];
 }
 
 void setup_git_env(const char *git_dir)