failure and fallback examples

Hi,

For ongoing ACTION-63 (HTTP examples) and towards ACTION-80
(rationale), I've added some examples of what happens in each
situation if the UA or the server is unaware of the methods
(server-parsed fragments, time ranges, range-refer) relevant to each
example:

http://www.w3.org/2008/WebVideo/Fragments/wiki/HTTP_Examples

Please proof-read and provide feedback. There are likely to be some
editing errors as many of the example scenarios are similar but subtly
different.

cheers,

Conrad.