Fixes parsing of invalid UTF-8 characters

[ce-manalang]

Followed advice from http://stackoverflow.com/a/8873922

[cjohansen]

So this basically ignores invalid utf-8 characters? Wouldn't it be better to fix them in the source files?

[ce-manalang]

@cjohansen yes we can fix the source files but if we want to juice a lot of js files with too many invalid chars, we have to go through them one by one.

Is it a good compromise if we just add a warning while juicing a file with invalid chars that those chars will be ignored? That way, juicing problematic files won't error out but it will not just silently juice.

Thoughts?

[cjohansen]

Warnings are a good compromise :)