os/server: Fix indentation
os/server: Fix TCP connection

- remove unused errno
- remove unused port_end
- correct calculation of addr_len
- use correct string length during IP copy
os/server: Fix possible port overflow

- add documentation about port being optional
- parse port into long and check for valid value
Merge #874 'fix TCP connection (issue #870)'
os_open: impl mch_open with libuv. ref #133

- use return value instead of open_req.result
- libuv uv_fs_open() returns `-errno` instead of always -1
- libuv always sets open_req.result to the return value, _except_ for OOM
  where it only sets the return value. So always use the return value.
- replace calls to mch_open macro.
- update call sites expecting -1 error
os_open: add unit tests
Merge #846 'impl mch_open with libuv'
Use default busted pattern for unittests

- Unittest should contain substring '_spec' in filename.
- This is the simplest way to use both lua and moonscript tests.
- This prevents running of non-test scripts from test folder.