Handle normalization of directory names correctly in wxFileHistory.

Don't use relative path for the directories, which can also be managed by
wxFileHistory, because they don't have any and the old code resulted in
showing an empty string for them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76179 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775