[ hTags ] fix include path to find "undefined.h"
[ tags ] fixed broken tags targets
[ fix ] added missing constructorForm in LHS.Unify
[ sharing ] resurrected pointer term representation

Type checking times are more or less the same,
slightly slower type checking (of std lib), but faster
serialisation.

Big win is actual call-by-need compile-time evaluation.
[ sharing ] updated error messages and interaction output

Things get more evaluated now, since evaluation gets shared.
[ sharing ] added more missing ignoreSharing
[ sharing ] updated error messages again