Another round of tweaks

Notable changes:
- Change a bunch of uses of memcmp(3) to compare strings (which can
  cause buffer read overflows) to strncmp(3).
- src/cmd/ksh93/include/name.h: Eliminate redundant Nambfp_f type.
  Replace with Shbltin_f type from libast's shcmd.h. Since that is
  not guaranteed to be included here, repeat the type definition
  here without fully defining the struct (which is valid in C).

src/cmd/ksh93/include/name.h

@@ -31,7 +31,8 @@
 #include	<ast.h>
 #include	<cdt.h>
 
-typedef int (*Nambfp_f)(int, char**, void*);
+typedef struct Shbltin_s Shbltin_t;
+typedef int (*Shbltin_f)(int, char**, Shbltin_t*);
 
 /* Nodes can have all kinds of values */
 union Value
@@ -54,7 +55,7 @@ union Value
 	struct Ufunction 	*rp;	/* shell user defined functions */
 	struct Namfun		*funp;	/* discipline pointer */
 	struct Namref		*nrp;	/* name reference */
-	Nambfp_f		bfp;	/* builtin entry point function pointer */
+	Shbltin_f		bfp;	/* builtin entry point function pointer */
 };
 
 #include	"nval.h"
@@ -149,7 +150,7 @@ struct Ufunction
 #define is_abuiltin(n)	(nv_isattr(n,NV_BLTIN|NV_INTEGER)==NV_BLTIN)
 #define is_afunction(n)	(nv_isattr(n,NV_FUNCTION|NV_REF)==NV_FUNCTION)
 #define	nv_funtree(n)	((n)->nvalue.rp->ptree)
-#define	funptr(n)	((Shbltin_f)(n)->nvalue.bfp)
+#define	funptr(n)	((n)->nvalue.bfp)
 
 /* NAMNOD MACROS */
 /* ... for attributes */