don't work consistant;
BLI_makestringcode()
This one works correct for paths that go up; it then makes a relative
path like : //../lib/file.blend
BLI_convertstringcode()
This one delivers different paths when it expands, the previous case
will just append the relative path, like /work/project/../lib/file.blend.
That string cannot be compared with the original... which happened to find
out if a library was read already.
Solution for now is that only the relative paths are compared, but it
won't work if multiple relative levels are used... like for libraries
that link recursive. To solve that, the entire 'relative' concept has to
be redesigned.
cb57d03e97