Properly handle recursion in recurse()

The restructuring of recurse() in the last few weeks actually broke
the recursion-flags in different tools.
As a long-term goal, the recursor should have a field "maxdepth"
which should be "1" for the non-Rflag-case. "0" stands for unlimited.

fs.h

@@ -19,6 +19,7 @@ struct recursor {
 enum {
 	SAMEDEV  = 1 << 0,
 	DIRFIRST = 1 << 1,
+	NODIRS   = 1 << 2,
 };
 
 extern int cp_aflag;