0031763: Foundation Classes - reporting of progress within parallel algorithms

0031763: Foundation Classes - reporting of progress within parallel algorithms

Classes Message_ProgressRange and Message_ProgressScope are improved to store start point of the range.
Method Message_ProgressScope::Value() is improved to compute the value in the current scope from the actual current value of the global progress.
Description of Message_ProgressScope class is improved.

Off-topic:
- method Message_ProgressScope::Relieve() is renamed to Close() for semantic consistency
- article in Upgrade Guide is revised and corrected