Merge remote-tracking branch 'atgeirr/fully-implicit' into fully-implicit
Prefer BOOST_CHECK_EQUAL to BOOST_CHECK

The former is more assertive than the latter and provides better
diagnostics.  Incidentally, switching to *_EQUAL() also fixes an
assignment that was (probably) intended to be an equality test:

   BOOST_CHECK(count = num)

in both test cases.
Include <cassert> for assert() macro.
Merge remote-tracking branch 'bska/fully-implicit' into fully-implicit
Add well contributions to mass balance residuals.