Fix the search iterator

It was all wrong, based on wrong assumptions I infered from the
documentation. I was able to understand it from this page:

  https://developer.atlassian.com/display/JIRADEV/JIRA+REST+API+Example+-+Query+issues

Also, now we defer the first POST(/search) request until the first
invocation of the next_issue method. The set_search_iterator method
doesn't POST anymore.
Check PUT and POST 'value' argument

It's easy to forget about the 'query' argument (which is the second one)
and pass the value as it instead of as the third argument.