Check dataunit releasing in frontend

[tomas-knap]

As described in https://team.eea.sk/jira/browse/COMSODE-200:

RDFQueryView.java:281
RDFQueryView.java:149
ManagableRdfDataUnit is created but never released.
It is mandatory to call .release() after work is done (especially problem for virtuoso data units).

Please check whether this is still relevant (w.r.t. to the currently prepared Virtuoso branch). If not, close with won't fix.

Should be assigned to Petr Skoda.

[skrchnavy]

@skodape : ist this issue still relevant? it could be related to virtuoso support.

[skodapetr]

It should be quick-solved by:
2be7174
ab6f76b

Problem is, that there is no space reliable enough to close the repository, also close and open too much will cause performance issue. For this reason the repository is auto closed after some inactivity (frost commit).
Other problem was during redeploy - where repositories had not been closed and the lock prevented from browsing until full tomcat restart. I hope that this is solved by the second commit.

[tomas-knap]

There is a checker, which closes open connections, solves the problem with RDFQueryView