fix FrequencySet.getFrequency in case sortedList is not sorted yet. closes #559
fix FrequencySet.getFrequency in case sortedList is not sorted yet. closes #559

tgvaughan/beast2,CompEvol/beast2,tgvaughan/beast2,tgvaughan/beast2,Anaphory/beast2,CompEvol/beast2,tgvaughan/beast2,CompEvol/beast2,Anaphory/beast2,Anaphory/beast2,CompEvol/beast2,Anaphory/beast2