Build against hmat library, it has been released

Install libhmat-oss.so library along with libOT.so so that it is
found when running tests.

distcheck ok.

git-svn-id: https://svn.openturns.org/openturns/branches/hmatrix@4145 59136d6a-6dff-0310-91ca-bfc5db6e1932