use Database-Transactions
added protection against multiple transaction-starts
added function documentation
transaction-support for PostgreSQL added
tidier implementation + bugfix
each request should be a transaction
Transaction functions throw dbExceptions now
committing a Transaction is done now within try-block
copy and paste errors corrected
begin_transaction in mysqli started in php5.5 - alternative implemented
another typo
Move beginTransaction
Merge pull request #1 from mattab/patch-1

Move beginTransaction
rename variable according coding standard
secure transactions against nesting
reverted Pgsql.php to old state ( unsupported )
fix missing paranthesis
Mark some methods in Visualization class to be exposed in developer docs.
Documentation tweaks.
Small refactor of the Login/Auth object.

Refs https://github.com/piwik/piwik/pull/299 - instead of creating loginFlow object, maybe we can throw events from the methods `processFailedSession()` and `processSuccessfullSession()`
Only use transactions for bulk requests (more than one request)
New config setting bulk_requests_use_transaction=1


; Whether Bulk tracking requests will be wrapped within a DB Transaction.
; This greatly increases performance of Log Analytics and in general any Bulk Tracking API requests.
bulk_requests_use_transaction = 1