Split async.h into multiple headers. (dm)


git-svn-id: svn://mielke.cc/main/brltty@7786 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Move the command execution code out of brltty.c (into cmdqueue.c). (dm)


git-svn-id: svn://mielke.cc/main/brltty@7787 91a5dbb7-01b9-0310-9b5f-b28072856b6e
On Windows, set INVALID_SOCKET_DESCRIPTOR to INVALID_SOCKET (instead of hard-coding -1). (dm)


git-svn-id: svn://mielke.cc/main/brltty@7788 91a5dbb7-01b9-0310-9b5f-b28072856b6e