Updated the definition of BEMPP_TEUCHOS_LIBRARY.

It reflects the library name change teuchos -> teuchoscore in Trilinos 11.
checkConsistency() no longer requires rhs.dualSpace() to be defined.
Fixed a compilation error in 32 bit mode (issue #160).
Fixed a memory leak in NonseparableNumericalTestKernelTrialIntegrator (issue #165).
Cleaned up the BemppConfig.cmake.in file.

Removed some old commented lines and the BEMPP_LIBRARY variable. The latter is
not set properly during installation since at CMake configure time libbempp.so
doesn't exist yet and so can't be found. But the BEMPP_LIBRARY_DIR variable is
set correctly and so CMakeLists.txt files can use

find_library(BEMPP_LIBRARY bempp PATHS ${BEMPP_LIBRARY_DIR})

to find the library (this is e.g. how the "Custom operators" example is
implemented).