Add --describe-candidates

[mppf]

In working on a Chapel program recently, I ran into a situation where I was having trouble seeing why a particular candidate didn't resolve for a call. Today, we describe the detailed reason for a call failure when printing the first candidate. But, the candidate I was expecting to match was a later candidate, and so the details weren't printed out. I was able to work around this issue and find the problem. However, it would have been easier if I had a way to ask the compiler to describe all of the candidates.

This PR adds a flag, --describe-candidates, that asks the compiler to print the detailed reason for a call failure when printing any candidate.

• check if the name is good
• should it print out a note, similar to what we have now for note: and 2 other candidates, use --print-all-candidates to see them
• add to the chpl man page
• full comm=none testing