Fix for ACT-2166:
Missing ${prefix} before ACT_ID_MEMBERSHIP in script /org/activiti/db/mapping/entity/Task.xml
Fix for ACT-1900 RuntimeService.getVariables(String, Collection) fetches all variables from DB
+ various optimization when accessing variables. Docs will follow.
Merge branch 'master' of https://github.com/Activiti/Activiti

# By Tijs Rademakers (3) and others
# Via Tijs Rademakers
* 'master' of https://github.com/Activiti/Activiti:
  Manually merge pull request 466
  Changed back to info logging
  Merge pull request 392 + fix multi tenant mail remaining configs
  remove unnecessary semi-colons
  Rework XML parsing of WSDLImporter using the J2SE standard way instead of using directly Xerces classes. Caution: this commit remove the dependency on Xerces, the DOM parser of the J2SE will be used. If Xerces is required, just re-add it as dependency in the POM.
  Minor log improvements
  Serialization support in order to use hazelcast as distributed cache.
Docs for "ACT-1900 RuntimeService.getVariables(String, Collection) fetches all variables from DB"