Added helpefull message for DomainError

Some functions throw DomainError for Real arguments because of type
stability and that the correct answer is complex. This patch add a ugly
hack, inspecting the bactrace, to give newcommers a helpefull hint. It
also document some of the functions that throws DomainError for negative
Real arguments.
Merge pull request #4249 from ivarne/DomainError_help

Added helpfull message for DomainError