Add section `before_install` in `.travis.yml` to create test group and
add current user to this group.
It is needed because by default user on Travis-CI belongs only to one
primary group derived from that user. So we have no alternative to
change group of the file.
Move tests of path_full_dir_name to path_spec. It is only defined in path.h.
Not sure why this works most of the time (I can only trigger a failure when
running under lldb).
It's a more logical place to have the test as well.
- 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.
