* cygwin.din: Export getpriority and setpriority.

	* cygwin.din: Export getpriority and setpriority.
	* fork.cc (fork_parent): Copy parent's nice value into child.
	* spawn.cc (spawn_guts): Ditto.
	* miscfuncs.cc (winprio_to_nice): New function.
	(nice_to_winprio): Ditto.
	* pinfo.cc (pinfo_init): If parent is not a Cygwin process, set
	default nice value according to current Win32 priority class.
	* pinfo.h (class _pinfo): Add nice member.
	* syscalls.cc (setpriority): New function, only implementing
	PRIO_PROCESS for now.
	(getpriority): Ditto.
	(nice): Just call setpriority.
	* wincap.h (wincaps::has_extended_priority_class): New element.
	* wincap.cc: Implement above element throughout.
	* winsup.h: Add prototypes for winprio_to_nice and nice_to_winprio.
	* include/limits.h (NZERO): New define.
	* include/cygwin/types.h (id_t): New datatype.
	* include/cygwin/version.h: Bump API minor version.
	* include/sys/resource.h: Add PRIO_XXX defines and prototypes for
	getpriority and setpriority.