In some situations when an application uses a lot of file descriptors (like > 1024), event handling in gpgme fails miserably.

As a library, it is better to use poll instead of select.

There are (relatively minor) corner cases for portability in difference between poll and select (about regular files, /dev/null, sockets, and what event is detected how), but for the use cases in gpgme, this patch works well.

make check

test with gnupg test suite

test with more than 1024 fds