silence all gcc warnings

gui-x11/alloc.c

@@ -125,7 +125,7 @@ getXdata(Memimage *m, Rectangle r)
 
  	xm = m->X;
  	if(xm == nil)
- 		return;
+ 		return nil;
  
 	assert(xm != nil && xm->xi != nil);
 	

gui-x11/draw.c

@@ -36,8 +36,6 @@ memimageinit(void)
 void
 memimagedraw(Memimage *dst, Rectangle r, Memimage *src, Point sp, Memimage *mask, Point mp, int op)
 {
-	int didx;
-	Rectangle dr, mr, sr;
 	Memdrawparam *par;
 	
 	if((par = _memimagedrawsetup(dst, r, src, sp, mask, mp, op)) == nil)
@@ -182,7 +180,6 @@ return 0;
 ulong
 pixelbits(Memimage *m, Point p)
 {
-	Xmem *xm;
 	if(m->X)
 		getXdata(m, Rect(p.x, p.y, p.x+1, p.y+1));
 	return _pixelbits(m, p);

gui-x11/screen.c

@@ -20,13 +20,14 @@
 #define	Font	IFont
 #define	Screen	IScreen
 
-#include <u.h>
-#include <libc.h>
-#include <draw.h>
-#include <memdraw.h>
-#include <keyboard.h>
+#include	"u.h"
+#include	"lib.h"
 #include	"dat.h"
 #include	"fns.h"
+#include	"user.h"
+#include	"draw.h"
+#include	"memdraw.h"
+#include	"keyboard.h"
 #include	"screen.h"
 
 #undef time
@@ -684,7 +685,6 @@ static void
 xkeyboard(XEvent *e)
 {
 	KeySym k;
-	unsigned int md;
 
 	/*
 	 * I tried using XtGetActionKeysym, but it didn't seem to