Fix problems with Linux USB I/O: (dm)
   Probing a device often took up to three attempts.
   Use asynchronous input for all endpoint transfer types even if monitoring isn't being used.


git-svn-id: svn://mielke.cc/main/brltty@8118 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Dynamically assign real-time signal numbers (rather than hard-code SIGRTMIN). (dm)


git-svn-id: svn://mielke.cc/main/brltty@8119 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Add asyncClaimSignalNumber() and asyncReleaseSignalNumber(). (dm)


git-svn-id: svn://mielke.cc/main/brltty@8120 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Fix the asyncClaimSignal() logs. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8121 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Allow each async component to more easily define new global fields. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8122 91a5dbb7-01b9-0310-9b5f-b28072856b6e
Reorganize async_internal.h a bit. (dm)


git-svn-id: svn://mielke.cc/main/brltty@8123 91a5dbb7-01b9-0310-9b5f-b28072856b6e