parseSourceLine -- parses a source line
the argument must be a non-empty, valid source line with comments stripped
quoteWords - similar to words, but with special handling of double-quotes and brackets.
The handling double quotes and  is supposed to match: apt-0.6.44.2/apt-pkg/contrib/strutl.cc:ParseQuoteWord()
The behaviour can be defined as:
Break the string into space seperated words ignoring spaces that appear between "" or . Strip trailing and leading white space around words. Strip out double quotes, but leave the square brackets intact.