Issue 78

* unrelated javadoc updates in metadata parser
* added 'rest' to root error context to make clear which instance of command is used (where multiple exist with same simple name)
* updated error creation on generic failure to include full stack trace as message
I think it is nice and right to send a meaningful error message. I took a quick look on the new builder method and I forgot that printStackTrace method ( http://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#printStackTrace() ) would also print the  backtrace for the cause, sorry for that. Well, let me just know if you dont think it could be useful to to store that information in the server side too (for a later log analyses system could process it, specially if a user didn't report that and the problem occurs sporadically, for example )