Simplify code for ewens_diploid_probability.
Add infrastructure for computing only changes prs/pdfs.
Clear computations::flags before destroying root token.
Don't add terms with a large overflow error into the sum.
Move the full calculation into a separate function.
Stop creating and destroying a smart pointer for no reason.
Move probability_for_context_diff( ) into separate function.
Remove duplicate comment.
Only compute probability_for_context_full( ) in debug mode.
Fix error in debug code.
Don't increment and decrement the reference count.
Revert previous fix.
Don't rewrite index_var if its been freed before we get back.
We *do* need to reroot to the correct context!
Don't forget to handle zeros!
varable -> variable.
Only look at probability_heads, not the whole of token 0.
Remove zeros hack -- just used unhandled.
Remove unused pr_limit.
Try to handle truncation error in inc_probability( ).