e03d87 Better approach for 93f25328c15 and 28db040026.

Authored and Committed by konstantin 4 years ago
    Better approach for 93f25328c15 and 28db040026.
    
    Do not require to explicitly call FileSystemTemporary::discard_changes().
    Instead, I just added a flag to FileSystemTemporary class (keep_files_when_destroyed),
    which defines how to deal with temporary files after class instance is destroyed.