This moves the CONST replacement up before we turn the elements into a
single string. The advantage is that we don't have to worry about
splitting the string properly to find the CONST names as the elements
are already split for us.t
Fix to CONST with the math evaluator to toss a message and error with values out of acceptable range for ARCSEC and ARCCSC.
Tweak to _PI to add constexpr for speedier execution.
Fix to the math tests for the new (and unbuggy) values for ARCSEC and ARCCSC.