* 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.