Fix _getTransitiveClosure: there was maximum one parent class in the list

But if you have more than one parent class on top, with this fix all of
them are now in the list.
Fix syntax error when short_open_tag is enabled
Fix query2 parser star select issue

Variable were parsed by the parser class but never added to the query
object. Projection vars are now added to the object thus fixing the
resulting * queries.

This fix introduced another issue which was also fixed. When no
visible graph is found, the store invalidates the query by settings the
where clause to a false filter. Virtuoso does not like such queries
that have a valist in the select clause. It crashes with a out of mem
error. This was fixed by also settings the varlist to * again when the
query where clause gets falsified.
correcting code documentation in Database cache backen
Merge pull request #52 from kkda/feature/short_open_tag

Fix syntax error when short_open_tag is enabled
Merge pull request #48 from k00ni/fix_getTransitiveClosure

Fix _getTransitiveClosure: there was maximum one parent class in the list
fixing Virtuoso _execSQL function. Someone before forgot to add an @, which leads to warnings in the Cache
Merge branch 'develop' of github.com:AKSW/Erfurt into develop
fixing #58 by flatten the array
correcting documentation in QueryCacheFrontend
Fix coding standard for Turtle Adapter
Add versioning support for deleteMatchingStatements

Select matching statements prior deletion and assign those to the versioning event.
Fix history for graph

Only return top level actions
Add support for action metadata

Metadata can optionally be attached to actions. In order to do so, the current
action id is now returned when an action is started.
Fix versioning unit tests

Add new table name to store stub in order to fix unit tests that would fail because of missing table.
Fix deletion of metadata

When history is deleted for a graph, also the metadata needs to be deleted, which is done now.
Add support for store transactions

If backend adapter supports transactions (e.g. Virtuoso via ODBC)
handle transactions in backend, otherwise ignore.

The addMultipleStatements method now automatically starts a transaction
if no transaction was already started.

Also the backend method returns a boolean value whether addition was
successfull and the store class passes this value to caller.
Add transaction support for deleteMatchingStatements