Fixed representation of combined constructs, clauses with expressions, etc.

Fixed representation of combined constructs, clauses with expressions, and
added initial development for cancellation constructs.

dca04ef507ed1936b509264ec615ae18c2cf5a6f by Alexey Bataev

Added tests for new features

23b32f7b1afed878ca04d1b8f15e3c80fbc279f2 by Alexey Bataev