* os: add test for os.open_append
* fix unclosed file in test_eof (it made os.open_append fail only on windows, since it got the previous file content, because the file was locked, and os.rm could not delete it)
vlib is the term for all modules included by default with V and
maintained as part of the V source code repository.
Some included modules depend on third party libraries, and these are kept
separate in the thirdparty directory at the root level of the source
repository.