Fix remaining small memory leaks - fixes #76.

Conflicts:
	hermes2d/src/api2d.cpp
	hermes2d/src/discrete_problem.cpp
Fix of subdomains.

Conflicts:
	hermes2d/src/discrete_problem.cpp
Fix the merge & remove last occurences of ENABLE_VIEWER_GUI.
Tweaks of linearizer, vectorizer.
Few fixes.
Accelerate finding the element where a point lies.
Fix the looking for an element containing a point.
A few fixes.
Finish optimizations in get_pt_value.