poor error message on malformed media range

[GoogleCodeExporter]

I'm seeing this Accept header in the wild: 

`text/html,application/json;q=0.9application/xhtml+xml,application/xml;q=0.9,*/*
;q=0.8`

Note the `0.9application`, which I believe is an error and should be 
`0.9,application`. mimeparse.parse_media_range fails with `ValueError: invalid 
literal for float(): 0.9application/xhtml+xml`. I would expect instead an error 
message saying the header is malformed. Does mimeparse have a concept of strict 
and lenient parsing? Does it want one?

Original issue reported on code.google.com by whit537@gmail.com on 20 May 2013 at 3:44