Support synchronized block on different properties

[Matthias Schoettle]

Currently, a critical combined fragment is code-generated as a synchronized(this) block.

Instead, the constraint of the operand should be used instead of hard-coding it to this to allow to synchronize on other properties as well.

[Bo Dang]

Resolves #462: add ValueSpecification in critical fragment

→ <<cset 5f6dc00efd7a>>

[Jörg Kienzle]

Merged in issue/462 (pull request #149)

Resolves #462: add ValueSpecification in critical fragment

Approved-by: Jörg Kienzle [e-mail]

→ <<cset d5888d5b4d1d>>