Move type definitions from chan1.go to chan.go and select.go.
Remove underscores from names.
Make c.buf unsafe.Pointer instead of *uint8.

Change-Id: I75cf8385bdb9f79eb5a7f7ad319495abbacbe942
Reviewed-on: https://go-review.googlesource.com/4900Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>