Support setting _NET_WM_PID in X11 environments

Support is added for setting _NET_WM_PID automatically. This is to
support scripting of the window environment. For example, this makes it
possible to script opening a window with same CWD:

1. Retrieve the current window
2. (new) get PID of window
3. Check if it's Alacritty, find first child (presumably a shell), and
   get the child's cwd.
4. Spawn new instance of terminal with cwd.

Unaddressed in this commit is how this will coexist on a Wayland system.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
index be4cae33..0a3366ce 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -27,6 +27,9 @@
 #[macro_use] extern crate log;
 #[macro_use] extern crate serde_derive;
 
+#[cfg(any(target_os = "linux", target_os = "freebsd", target_os="dragonfly", target_os="openbsd"))]
+extern crate x11_dl;
+
 extern crate cgmath;
 extern crate copypasta;
 extern crate errno;