Inaccurate Accept parsing

[krizhanovsky]

From #1050: while we don't know all the possible content types we may only check syntax of the header and the RFC requires / in the type, so Req_I_AcceptOther must be fixed. invalid/foo, invalid/* - are allowed, invalid/ or invalid - aren't.

Also please update the HTTP parser unit test by the Date cases and select appropriate checkboxes in #1059 corresponindinf to date headers. No need to port the fix to 0.6.