Several improvements / corrections in syscheck:

- Report file deletion, even without realtime enabled
- Report modifications made on directories
- Corrects bug so that files created between the first and second scan
  are reported as new files
- Corrects bug that made changes reverting a file to the state it was
  in when ossec started unreported
- Avoids computing hashes multiple times to improve performance
- Make the time between two syscheck wakeups configurable in
  internal_options
Correct bug introduced in last commit, ignoring user specified syscheck
frequency
get rid of warnings
corrects bug for deleted files when scan_on_start=no