w32: Merge all the object tables of w32-io into one.
* src/w32-io.c (fd_table_size): New. Used in most places instead of the MAX_SLAFD constant. (reader_table, writer_table, notify_table): Merge them into ... (fd_table): this table. Chnage all affected code to take just one lock.
- Signed-off-by: Werner Koch <wk@gnupg.org>