fixed 'getSliceContents'
do not throw an exception when some slices were overwritten
changed default positioning strategy:
  added special handling for JetObjectLiteralExpression
unified JetVisitor & JetVisitorVoid
added JetVisitorVoidWithParameter
added CFPContext to avoid recreating of CFPVisitor all the time;
used JetVisitorVoidWithParameter
fixed exponential building of cf graph
if there was en error in chained qualified expression
fixed bug in renderer for violated upper bound error