bugfix for non-pointed cones of dimension 1

In the Fourier-Motzkin elimination the use of dim-2 lead to an error. Now F-M
is skipped for dim <= 1, it never has to compute something in this case.
slightly changed way of building

Create normaliz.o and link then with libnormaliz.a instead of compiling
and linking in one step. Makes normaliz executable faster to compile if
there where only changes in libnormaliz.
Some error messages in cone improved
dual mode: reduce completely

The elements are reduced with all reducers with smaller degree, not
only with those up to the half of the degree.
Matrix::vol_destructive error check corrected

There was one ! too much and therefore the errorcheck was done exactly if it
should not.