poll() bugs and patch

[Boris Schaeling]

There are several bugs in poll():
- poll() must return 0 if no descriptor is ready and the timer expires. It
works correctly if all descriptors are non-negative. Otherwise poll()
returns the count of negative descriptors which is wrong.
- The implementation of poll() must call cygwin_select() even if all
descriptors are invalid. Currently poll() returns immediately - and ignores
any timer value. The return value is wrong again because of the bug above.
- If the timer expires revents must be 0 and must not be set to anything
else like POLLNVAL, POLLHUP or whatever.
- If cygwin_select() returns -1 revents must be 0 and must not be set to
POLLERR. Eg. a signal interrupting poll() doesn't mean an error has occured
for a TCP connection.
- If an error is pending revents must be set to POLLERR.
- The implementation of poll() has a local variable called open_fds that
isn't used. I can't see why this variable exists.

I've attached three files:
- newpoll.cc has a new implementation of poll() which fixes the bugs.
- patch.cc is the patch.
- polltest.c is a testcase.

I rebuilt cygwin1.dll with my poll() function so there should be no problems
when compiling.

Boris
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