git-clean: fix the description of the default behavior

Currently, when called without -n and -f, git clean issues

fatal: clean.requireForce not set and -n or -f not given; refusing to clean

which leaves the user wondering why force is required when requireForce
is not set. Looking up in git-clean(1) does not help because its
description is wrong.

Change it so that git clean issues

fatal: clean.requireForce defaults to true and -n or -f not given; refusing to clean

in this situation (and "...set to true..." when it is set) which makes
it clearer that an unset config means true here, and adjust the
documentation.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-clean.txt

@@ -33,8 +33,8 @@ OPTIONS
 
 -f::
 --force::
-	If the git configuration specifies clean.requireForce as true,
-	'git clean' will refuse to run unless given -f or -n.
+	If the git configuration variable clean.requireForce is not set
+	to false, 'git clean' will refuse to run unless given -f or -n.
 
 -n::
 --dry-run::

builtin-clean.c

@@ -67,8 +67,8 @@ int cmd_clean(int argc, const char **argv, const char *prefix)
 		die("-x and -X cannot be used together");
 
 	if (!show_only && !force)
-		die("clean.requireForce%s set and -n or -f not given; "
-		    "refusing to clean", config_set ? "" : " not");
+		die("clean.requireForce %s to true and neither -n nor -f given; "
+		    "refusing to clean", config_set ? "set" : "defaults");
 
 	if (force > 1)
 		rm_flags = 0;