Freeciv

One in an endless series of Gtk3 theming bugs.

• giant handles for detaching panes
• tiny text

• I've not seen it with msys1 Gtk3 (3.8.2)
• I've not seen it on Linux with Gtk3 (3.10.8-0ubuntu1.6)
• cazfi has seen it on Linux with newer Gtk3 than that
• I've seen it with msys2 Gtk3 and Gtk3.22 clients (2.6.0-beta0+c8cad4d8dd; msys2 environment 170714; Gtk3 3.22.16)

I believe it's well-known that getting a single theme that works across all the Gtk3 versions that the Gtk3 client claims to support is hard-to-impossible.
cazfi: "One of the reasons gtk3.22-client was created is that its theme does not even try to be compatible with ancient gtk3."
That means we can fix this for the Gtk3.22 client, at least.
It's looking likely that this can be the supported (even preferred?) 2.6 Linux client. Windows will be at most Gtk3 until we move to msys2, but by the same token it will be old Gtk3.
So we can probably get this out of most users' way for 2.6.