This is a fork-and-subset of github.com/BurntSushi/xgb at git revision
3ac861bb (2015-04-26), plus additional manual patches (see below).

The subset consists of these directories:
github.com/BurntSushi/xgb
github.com/BurntSushi/xgb/render
github.com/BurntSushi/xgb/shm
github.com/BurntSushi/xgb/xproto

Other directories in the original github.com/BurntSushi/xgb repository are not
used by golang.org/x/exp/shiny, and were not copied to the vendor tree here:
github.com/BurntSushi/xgb/bigreq
github.com/BurntSushi/xgb/composite
etc
github.com/BurntSushi/xgb/xvmc

Additional manual patches:
https://go-review.googlesource.com/#/c/12765/
edits:
xproto/xproto_test.go
to skip tests that fail on Darwin.
