Disable mysql bin log by default

[kirtangajjar]

Turns out bin log can quickly fill up your disk space. Also, the primary uses of binary log are:

* For replication, the binary log on a master replication server provides a record of the data changes to be sent to slave servers...
* Certain data recovery operations require the use of the binary log...

In case someone might want bin log for 2nd use case, he/she can enable it manually. It's best to disable this feature as most of the time it won't be necessary(AFAIK).