Accept header parsing fixes. Now return first acceptable match rather than last. If not acceptable match in accept, 406 error returns list of acceptable types as text string. application/xml is listed in acceptable types only if dicttoxml is installed. Handle q > 1.0 by demoting q factor to 0.0001 making it unusable. Test cases for all this code. XML is commented out as we don't install dicttoxml.py.

{
    "validthis": true,
    "laxcomma" : true,
    "laxbreak" : true,
    "browser"  : true,
    "eqnull"   : true,
    "debug"    : true,
    "devel"    : true,
    "boss"     : true,
    "expr"     : true,
    "asi"      : true
}