Add check for arc4random.
Stir arc4random.
Rework installation logic.

If a file is found on the way do the following:
1) Append 12 chars random suffix to the filename;
2) Extract new file to that modified filename;
3) Rename new file to old file.
- or -
3) Remove temporary file in case of error.
Report about locked packages.

Suggetsed by:	az