sh: Call fc -e editor with interrupts enabled.

Starting the fc -e editor can execute arbitrary script, and executing
arbitrary script with INTOFF in effect may cause unexpected results.

This change (together with other changes) serves mainly to allow asserting
that INTOFF is not in effect when starting the evaluation of a node.

bin/sh/histedit.c

@@ -376,10 +376,10 @@ histcmd(int argc, char **argv __unused)
 		char *editcmd;
 
 		fclose(efp);
+		INTON;
 		editcmd = stalloc(strlen(editor) + strlen(editfile) + 2);
 		sprintf(editcmd, "%s %s", editor, editfile);
 		evalstring(editcmd, 0);	/* XXX - should use no JC command */
-		INTON;
 		readcmdfile(editfile);	/* XXX - should read back - quick tst */
 		unlink(editfile);
 	}