Fix issue #168: Evaluation of function at specific point

Using both absolute and relative check in numerical tests for
collisions with intervals, triangles, tetrahedrons:

const double eps = std::max(DOLFIN_EPS_LARGE, DOLFIN_EPS_LARGE*std::max(dx, std::max(dy, dz)));
Add collection of unit tests for issues reported for the geometry library
Add Issues.py to list of unit tests
Disable Issues.py/eval unit tests in parallel
Merge branch 'logg/fix-issue-168'

Conflicts:
	test/unit/test.py