Only add option for shared libraries once

The way the test was done previously, it was added for *every* option
after `--enable-shared`, not only that one.
Added method equals in BlackoilState.hpp
Added test with accompanying data for Blackoilstate::equals()
make redhat packaging compatible with el5
Merge pull request #417 from rolk/417_shared

Only add option for shared libraries once
Replaced include math.h with cmath, and changed from fabs to abs. Fixed an error in the testfile, a filename was wrong
Merge pull request #419 from flikka/blackoilstate-equals

Blackoilstate equals function, with tests and data