Added additional parameter to FileOutput flushInterval. This enables the use of and AND statement to flush data to disk if two requirements (time and number of messages) occurred.
Revert "Added additional parameter to FileOutput flushInterval. This enables the use of and AND statement to flush data to disk if two requirements (time and number of messages) occurred."

This reverts commit 54732f696fdb16910fff1b7c2fbd7be9eaf7b00c.
Added two new parameters 'flush_count' and 'flush_operator'.
Merge branch 'dev' of github.com:somergy/heka into somergy-dev
Final tweaks, added tests, docs and changelog update.
Merge pull request #681 from mozilla-services/fileoutput-flush-options

Fileoutput flush options