PBXContainerItemProxy were removed by xUnique

[truebit]

example project file: https://github.com/truebit/webkit/raw/master/Source/WebKit2/WebKit2.xcodeproj/project.pbxproj
xUnique this file. Then xUnique the modified the file.
The two xUnique result should be the same, but all PBXContainerItemProxy was deleted

@@ -1672,14 +1672,12 @@
/* End PBXBuildFile section */

/* Begin PBXContainerItemProxy section */
-       E27760424A6E143D2DEB0743C71566F0 /* PBXContainerItemProxy */ = {
            isa = PBXContainerItemProxy;
            containerPortal = C3AF0EBF34872303BA894413662CE63A /* Project object */;
            proxyType = 1;
            remoteGlobalIDString = E040A817DF5831FFE5479D666B299EB9;
            remoteInfo = WebKit2;
        };

[truebit]

Cause: method __unique_target_dependency used to uniquify PBXTargetDependency is wrong