add support for well known prefixes

[szydan]

Would be good if e.g "void" or "foaf" is used in a query
that there is no need to define a prefix

Here is an example list
http://sparql.sindice.com/sparql?nsdecl

Or the top X from prefix.cc

Cheers

[mhausenblas]

Sounds like a good idea, yeah, thanks @szydan