BUGFIX: Wrong pointer was passed in Instruction.replace_all_uses_with
FEATURE: Added successors property to BasicBlock to get list of successors blocks
BUGFIX: Added check whether terminator instruction has function to query for successors

It appears that the RET llvm instruction does not provide the getNumSuccessors and
getSuccessor function. Work around this by assuming that any instruction which does
not have the getSuccessor method just has 0 successors.
Merge pull request #115 from zaddach/master

Bugfix for replace_all_uses_with function and feature for getting successor blocks for a BB