There were two implementations of integer exponentiation. Merge them into a new
file under utils/cc/.
By the way, optimize it using exponentiation by squaring.
Note that dynare++ will only be built if configure finds ctangle, blas, lapack and pthreads
git-svn-id: https://www.dynare.org/svn/dynare/trunk@2922 ac1d8469-bf42-47a9-8791-bf33cf982152