clock:birthdeath and clock:coalescence with dated tips should give an error

[zhangchicool]

The clock:birthdeath and clock:coalescence priors do not handle dated tips (tips with ages larger than zero), if I understand the LnCoalescencePriorPr() and LnBirthDeathPriorPr() functions correctly. However, the program runs without throwing an error. I think the program should shop running and give an error to users to choose a different prior, e.g., clock:uniform or clock:fossilization.

[zhangchicool]

The coalescent prior has supported serially-sampled tips (#270) in commit 9036a0830ef63decf51fcb932d3ba6daf719128a