Use new continuation API for full text search

Mainly to future-proof, and to avoid the API sending us this
warning for every query we make:
  Formatting of continuation data will be changing soon.
  To continue using the current formatting, use the 'rawcontinue' parameter.
  To begin using the new format, pass an
  empty string for 'continue' in the initial query.

I found some hints for the new continuation API here:
http://www.mediawiki.org/wiki/API%3aQuery#Continuing_queries
Still, the documentation could have been better there if it had use actual
HTTP requests as examples.

Change-Id: I705f4db4855db4de4d062aa2ac808fcfe0cecb99
Merge "Use new continuation API for full text search"