Constraints can override their own number of solver iterations (either more or less than the default) or leave it default (-1)

Bump version to 2.80

src/LinearMath/btScalar.h

@@ -28,7 +28,7 @@ subject to the following restrictions:
 #include <float.h>
 
 /* SVN $Revision$ on $Date$ from http://bullet.googlecode.com*/
-#define BT_BULLET_VERSION 279
+#define BT_BULLET_VERSION 280
 
 inline int	btGetVersion()
 {

src/LinearMath/btSerializer.h

@@ -437,8 +437,8 @@ public:
 
 
 			buffer[9] = '2';
-			buffer[10] = '7';
-			buffer[11] = '8';
+			buffer[10] = '8';
+			buffer[11] = '0';
 
 		}