Pull request #710 correctly noted that TreeDirNode directories must
be passed to "globpath()" as relative paths (i.e., to the working
directory) if 'wildignore' rules for relative paths are to be
obeyed.
The solution was to use "fnamemodify()" to get a relative path to
the TreeDirNode object's directory, if possible. However, this
method does not modify our TreeDirNode path if it IS the current
working directory. Thus, immediate children of the node are seen as
absolute paths in glob results when our PWD is pointing to their
parent. This is not consistent behavior.
This commit defines the result of this function as ',' when this
special case arises to fix this problem.
See ":h 'path'" for an explanation of how this works.
b0c44c7be1