unix: fix handling error on UDP socket creation
unix, windows: remove unneeded define
unix, windows: be consistent when binding implictly in UDP

Only these functions will trigger an implicit binding of a UDP handle:
- uv_udp_send
- uv_udp_recv_start
- uv_udp_set_membership

All other functions will return UV_EBADF in case the socket was not
bound.

Note: currently the socket is created and bound at the same time. This
may change in the future.
unix: fix uv__open_cloexec usage

It returns the fd or the negated errno.
doc: refer to README.md to find out more information about tests

Reason for this change is because 'make test' command does not work.

Signed-off-by: Luka Perkov <luka.perkov@sartura.hr>
process: adjust quote_cmd_arg for empty arguments

adjust quote_cmd_arg so that empty command line
arguments are double quoted instead of skipped
win: minor coding style cleanup
win: open_named_pipe const argument
unix, windows: uv_dlerror const argument
unix, windows: avoid error in uv_fs_event_stop

For consistency with other handle types, if stop is called while the
handle wasn't started yet, it's a no-op.
unix: simplify how process handle queue is managed
unix: stop child process watcher after last one exits