Parser doesn't return useful position information on error

[cespare]

Right now the error shown to the user when you try to generate from an invalid thrift file only says the offset (not the filename, line, or column).

I've fixed this issue on my branches of go-thrift and go-parser. I don't have time right this minute to formulate them into a proper pull request, and I'm not sure you'd want to do it this way anyway (it requires changes to both of the repos together).

You can see what I did here:

https://github.com/ooyala/go-parser/commit/9a7e0d630d609f1b98755259a7a5272cf973a063 https://github.com/ooyala/go-thrift/commit/997808dbaab756cc678be7013fecf432f54695a0