- implemented IOCTL_SERIAL_WAIT_ON_MASK for DeviceIoControl
  on serial lines in ntdll
- now using thread pool (instead of simple thread) for the
  background operations (this should help some high load
  situations)
- used this to implement WaitCommEvent on top NtDll functions
- in kernel32, removed now the no longer used termios/ioctls...
  for comm devices

has been asked for, and sets all the others to zero (with conformance
test).

the former are exported by rpcrt4 seemingly to allow callers of tower
functions to free the allocated memory.

field so cast it to DATABLOCK_HEADER to access the dwSignature
field. Fixes the compilation with Visual C++ on Windows.

explorer: Split the device management to a separate file to make it usable independently of HAL support.