Gaelmuller syscheck improvemnts

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

Orginal Pull Request: https://bitbucket.org/jbcheng/ossec-hids/pull-request/19/several-improvements-corrections-in/diff

@gaelmuller