ufc needs Python 2, but Python 3 may be found (with fix)

Hi,

I tried to compile ufc on another machine today and got the error messages

============================== *snip* ==============================
[...]
[ 50%] Building CXX object CMakeFiles/_ufc.dir/src/ufc/ufcPYTHON_wrap.cxx.o
/usr/bin/c++ -D_ufc_EXPORTS -O3 -DNDEBUG -fPIC -I/homes/numerik/nschloe/Work/FEniCS/src/ufc/src/ufc -I/usr/include/python3.2mu -o CMakeFiles/_ufc.dir/src/ufc/ufcPYTHON_wrap.cxx.o -c /homes/numerik/nschloe/Work/FEniCS/src/ufc/dorsal_build_dir/src/ufc/ufcPYTHON_wrap.cxx
/homes/numerik/nschloe/Work/FEniCS/src/ufc/dorsal_build_dir/src/ufc/ufcPYTHON_wrap.cxx: In function ‘bool Py_convert_uint(PyObject*, std::size_t&)’:
/homes/numerik/nschloe/Work/FEniCS/src/ufc/dorsal_build_dir/src/ufc/ufcPYTHON_wrap.cxx:3288:46: error: ‘PyInt_AS_LONG’ was not declared in this scope
/homes/numerik/nschloe/Work/FEniCS/src/ufc/dorsal_build_dir/src/ufc/ufcPYTHON_wrap.cxx:3290:54: error: ‘PyInt_AS_LONG’ was not declared in this scope
============================== *snap* ==============================

This is because CMake spit out the Python3.2 include folder which doesn't have those symbols.
To make sure that Python 2 is found, add

set(PythonInterp_FIND_VERSION 2)

right before

find_package(PythonInterp QUIET)

in ufc's main CMakeLists.txt.

--Nico