SHELLERS for SYSCF, MacOS 10.5 hints file (trunk only)

Add SHELLERS - people allowed to use ! command with same syntax as WIZARDS.
Add new hints file for 10.5, since the rules and commands for groups changed
(new commands introduced in 10.4, old ones removed in 10.5; creating a new
user under 10.4 gave you a matching group, in 10.5 it doesn't).  Also move
shared build into roughly right place in file system when being installed
for root - don't use ~root.
Makefile.top - don't remove ./-p unless it exists (that's always annoyed me).
fix error invoking macosx.sh

include/extern.h

@@ -2322,6 +2322,7 @@ E void NDECL(port_help);
 # endif
 E void FDECL(sethanguphandler, (void (*)(int)));
 E boolean NDECL(authorize_wizard_mode);
+E boolean FDECL(check_user_string, (char *));
 #endif /* UNIX */
 
 /* ### unixtty.c ### */