cp: Rename -d option to -P

The -d option is a GNU extension and is equivalent to its "-P
--preserve=links" options.

Since we don't implement the --preserve=links functionality anyway (it
means preserve hard links between files), just call it -P, which is
specified by POSIX.

Additionally, there is no need to check for cp_Pflag again before
copying the symlink itself because the only way the mode in the stat
will indicate a symlink is if we used lstat (which we only do if -P is
specified).

cp.c

@@ -19,10 +19,10 @@ main(int argc, char *argv[])
 	ARGBEGIN {
 	case 'a':
 		/* implies -dpr */
-		cp_aflag = cp_dflag = cp_pflag = cp_rflag = 1;
+		cp_aflag = cp_Pflag = cp_pflag = cp_rflag = 1;
 		break;
-	case 'd':
-		cp_dflag = 1;
+	case 'P':
+		cp_Pflag = 1;
 		break;
 	case 'p':
 		cp_pflag = 1;