ACT-1418 Unit tests and suggested fix for NPE on uncaught error event

Work done at Hackergarten Vienna together with @rafacm and
@florianpirchner
Fix distro build
Merge branch 'master' of https://github.com/Activiti/Activiti
Added unit tests + fixes for feedback step type of simple workflow
Added form key to historic task instance
ACT-1580: added simple unit test
Fix for history form key storage
ACT-1583: Json for feedback step
Merge branch 'master' of github.com:Activiti/Activiti
ACT-1577: Index ACT_IDX_HI_ACT_INST_PROCINST should use EXECUTION_ID_ instead of PROC_INST_ID_
Adding logic/logging for randomly-faling ServiceTaskSpringDelegationTest
Fix for ACT-1586: ExecutionQuery returns wrong results when using multi instance on a receive task
Merge branch 'master' of github.com:Activiti/Activiti
Docs for ACT-998 + added script execution listener
Merge with master
Merge branch 'ACT-1418' of https://github.com/pebrc/Activiti into pebrc-ACT-1418
Merge branch 'master' of github.com:Activiti/Activiti
ACT-1555: accepted 2 pull-requests, tests now fixed
Added Camel task to user guide
Merge branch 'master' of https://github.com/Activiti/Activiti