Better error message for "Failed to load meta for ... : Error: ENOENT: no such file or directory, open 'compiled/source/transpiled/....'

[cboulanger]

The above message basically means: there is a symbol in the code that has no corresponding class definition. As it is, qooxdoo newcomers will have a hard time understanding what went wrong. A better error message could output the file and line number where the symbol was found and explain what the problem is.