core: Handle ‘etag’ and ‘kind’ members in JSON feeds

Set the GDataFeed:etag property and ignore the kind.
tasks: Handle an additional form of AUTHENTICATION_REQUIRED error

Apparently there are two ‘reason’ codes which correspond to this.
tasks: Add preconditions for tasklist IDs being set when inserting tasks

Can’t insert a task to a non-tasklist.
docs: Fix a typo in the README
tests: Remove unnecessary non-NULL test

It was confusing Coverity.

Coverity issue: #74584
Add --disable-tests to skip the building of tests

https://bugzilla.gnome.org/show_bug.cgi?id=739395
core: Eliminate ISO 8601 formatting workaround for dates

Google have fixed the issue upstream, so the workaround is no longer
needed. Thanks Google!

https://bugzilla.gnome.org/show_bug.cgi?id=737799
https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3595
tests: Temporarily disable some Contacts test assertions

Seems these elements broke on the server at some point.

https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3662
Release version 0.16.1