Domain violations for sec, csc, cot on valid domains.

[mewilhel]

These functions are defined as composites using the inverse (e.g. cot(x::MC)= inv(tan(x))) which results in domain violations on intervals tighter than Interval(0, pi).

The fix here is to add definitions for sec, csc, cot, asec, acsc, acot that aren't defined as composites. Basically, check for domain violations and return nan(x) if this is the case. Otherwise, compute the envelope. This would also require explicit definitions of these functions in IntervalArithmetic.jl since cot(x::Interval) has the same issue.