Remove performance penalties for "check steady state"

Current Situation:
If you set the parameter

• check_steady_state_of_files = true
• check_steady_state_interval = 2
• check_steady_count = 30

then the source files are checked for max 30 times (check_steady_count) wether the file size has changed between an interval of 2 seconds (check_steady_state_interval).

This feature works (tested for webdav, ftp, sftp) but includes performance penalties.

For example, when using 100 source files then this check requires at least 100*check_steady_state_interval seconds because the wait interval is applied to each file.

Desired Situation:
The function checks all (unsteady) source files after one interval.