Merge branch 'grubba/fdlib' into 8.1 * grubba/fdlib: I/O [NT]: Moved FD_SETSIZE definition to global.h. I/O [NT]: Use new low-level functions from Process. I/O [NT]: Added some assertions. I/O [NT]: Added serialization of access to fd handles. I/O [NT]: Use the new low-level functions. I/O [NT]: Added some low-level fd handling functions. Build [NT]: Fix typo of EACCES. I/O [NT]: Document some internal data structures.