Stop using GAP_ROOT_PATHS

[Max Horn]

Some files in fining still use GAP_ROOT_PATHS; they should use GAPInfo.RootPaths instead (same holds for the forms package, by the way)

[Jan De Beule]

All occurrences of GAP_ROOT_PATHS have been removed or changed into GAPInfo.RootPaths. Some files in the repository that are not part of the release (files in the ./old directory), may still contain GAP_ROOT_PATHS. But files in this directory are never distributed.