Require inputproto 2.4 to build the gesture support
Replaces !25 (closed) with a slightly more lenient version: where inputproto 2.4 isn't available the gesture support won't be enabled. We only have two use-cases we need to care about:
- building against a server with gesture support, in which case we can expect inputproto 2.4 because the server requires it
- building without inputproto 2.4 in which case we can't have a gesture-enabled server anyway
Theoretically we should use
abi_xinput is a single string and we'd have to split that using shell and... urgh. So let's just add another ifdef.
The case of having a server with gesture support but inputproto is still on 2.3 is a system setup issue that we shouldn't need to special-case.