Bump to 0.17.1

Start a new development cycle.
Require GLib >= 2.37.6

We're going to need the latest snapshot.
tests: Use the new TAP support in GTest

Instead of using the old GLib test harness, we should use the newly
added TAP support and the TAP driver inside autotools.
path: Remove unused variable
Remove compile time GLib version check

We depend on a new version of GLib, so we can remove a bunch of old
version checks.