[vtkusers] OS X 10.7.3 breaks building KwSys in VTK and ITK

[Kent Williams]

This is one of those 'oh great' moments. I updated my Mac to 10.7.3
and ITK and VTK compiles broke, with this error:

In file included from
/scratch/kent/ants/brainsia/build/ITKv4/Modules/ThirdParty/KWSys/src/KWSys/SystemTools.cxx:26:
/scratch/kent/ants/brainsia/build/ITKv4-build/Modules/ThirdParty/KWSys/src/itksys/ios/sstream:176:29:
error: cannot initialize a
      parameter of type 'iostate' (aka 'std::_Ios_Iostate') with an
lvalue of type 'int'
    this->IStrStream::clear(flags);
                            ^~~~~
/usr/include/c++/4.2.1/bits/basic_ios.h:133:21: note: passing argument
to parameter '__state' here
      clear(iostate __state = goodbit);

The problem is that the function signature for ios::clear changed
between 10.7.2 and 10.7.3 -- and for some reason the compiler won't do
the conversion between int and iostate.

It's vexing to me because I can't imagine ever calling ios::clear()
with an argument.  Clear is clear, right?