scriptexec: try to use shell/interpreter name as well on OS/2

If specified path does not exist, try to use shell/interpreter name
without directory.

On OS/2, directory structures of distribution is quite different. And
Some scripts have hard coded shell/interpreter. To overcome this, allow
to use shell/interpreter name if specified path does not exist.

exec.c

@@ -957,6 +957,14 @@ scriptexec(struct op *tp, const char **ap)
 			if (*cp)
 				*tp->args-- = (char *)cp;
 		}
+#ifdef __OS2__
+		/*
+		 * Use shell/interpreter name without directory if specified
+		 * path does not exist
+		 */
+		if (ksh_vstrchr_dirsep(sh) && !search_path(sh, path, X_OK, NULL))
+			sh = _getname(sh);
+#endif
 		goto nomagic;
  noshebang:
 		m = buf[0] << 8 | buf[1];