Method findDefinitionPoint

Set the basic block, \b defblock, and PcodeOp, \b defpoint, where they are defined. Its possible that \b lo and \b hi are \e input Varnodes with no natural defining PcodeOp, in which case \b defpoint is set to null and \b defblock is set to the function entry block. The method returns \b true, if the definition point is found, which amounts to returning \b false if the SplitVarnode is only half co