N°2793 Log rotation (#117)

Now log file name is unchanged : current log is still /log/error.log \o/

Rotation check (using file last modification time) is done :
* on each file write : we don't want to miss calls if session last from 23:59:59 to 00:01 for example ! Though the filemtime() call is done once per session to lower performance impacts
* using a new background process (LogFileRotationProcess)

File renaming on setup is therefore removed.
Also the interface is renamed (from ILogFileNameBuilder to iLogFileNameBuilder) to conform to iTop convention.

core/config.class.inc.php

@@ -2071,7 +2071,6 @@ class Config
 			$bReturn = fclose($hFile);
 
 			utils::SetConfig($this);
-			FileLog::RenameLegacyLogFiles();
 
 			return $bReturn;
 		}