Change janice_errors.h so there's only one list of errors needed to g…

[taa01776]

…et enums, string names, and messages.
Also changed the harness code for registering nonfatal errors to use this. It's kind of an ugly include file hack, but it works to define the enum, an array containing the error names ("JANICE_OUT_OF_MEMORY"), and another array containing the error strings with only one entry of the actual error information.

Not strictly necessary, but I think it makes the error definitions cleaner.

[taa01776]

I notice the shorter-error-list pull request is still pending.
This might also be controversial, but I ran into a number of problems using the JanICE test harness executables, because they construct file names by concatenating strings in a fairly naive way: failed, for example, when I supplied absolute path names for images in a detection protocol file. I changed them to use boost::filesystem primitives to construct new path names instead.