Fix for two proxy + undo related crashes:

* When making a proxy, the lib linked IPO driver was also changed to
  point to the proxy object, and after undo this local proxy object
  was replaced so the pointer became invalid. In fact it is not needed
  at all to change this because the IPO code maps the pointer to the
  local proxy object already.
* Undoing the make proxy operation would crash because the proxy_from
  pointer in the library linked object would still point to the removed
  object. Now it clears all these pointers before undo, because on each
  undo memory file read they will be set again anyway.

source/blender/blenkernel/intern/object.c

@@ -1163,7 +1163,10 @@ static void copy_object_pose(Object *obn, Object *ob)
 			ListBase targets = {NULL, NULL};
 			bConstraintTarget *ct;
 			
-			if(con->ipo) {
+			/* note that we can't change lib linked ipo blocks. for making
+			 * proxies this still works correct however because the object
+			 * is changed to object->proxy_from when evaluating the driver. */
+			if(con->ipo && !con->ipo->id.lib) {
 				IpoCurve *icu;
 				for(icu= con->ipo->curve.first; icu; icu= icu->next) {
 					if(icu->driver && icu->driver->ob==ob)

source/blender/blenloader/intern/readblenentry.c

@@ -364,6 +364,9 @@ BlendFileData *BLO_read_from_memfile(const char *filename, MemFile *memfile, Ble
 	if (fd) {
 		strcpy(fd->filename, filename);
 		
+		/* clear ob->proxy_from pointers in G.main */
+		blo_clear_proxy_pointers_from_lib(fd);
+
 		/* separate libraries from G.main */
 		blo_split_main(&mainlist, G.main);
 		/* add the library pointers in oldmap lookup */

source/blender/blenloader/intern/readfile.c

@@ -1130,6 +1130,19 @@ static void change_idid_adr(ListBase *mainlist, FileData *basefd, void *old, voi
 	}
 }
 
+/* lib linked proxy objects point to our local data, we need
+ * to clear that pointer before reading the undo memfile since
+ * the object might be removed, it is set again in reading
+ * if the local object still exists */
+void blo_clear_proxy_pointers_from_lib(FileData *fd)
+{
+	Object *ob= G.main->object.first;
+	
+	for(;ob; ob= ob->id.next)
+		if(ob->id.lib)
+			ob->proxy_from= NULL;
+}
+
 /* assumed; G.main still exists */
 void blo_make_image_pointer_map(FileData *fd)
 {

source/blender/blenloader/intern/readfile.h

@@ -112,6 +112,7 @@ FileData *blo_openblenderfile( char *name, BlendReadError *error_r);
 FileData *blo_openblendermemory( void *buffer, int buffersize, BlendReadError *error_r);
 FileData *blo_openblendermemfile(struct MemFile *memfile, BlendReadError *error_r);
 
+void blo_clear_proxy_pointers_from_lib(FileData *fd);
 void blo_make_image_pointer_map(FileData *fd);
 void blo_end_image_pointer_map(FileData *fd);
 void blo_add_library_pointer_map(ListBase *mainlist, FileData *fd);