Allow a regular file to be set as the root directory for local and remote
file browser sheets, which will then use the parent of the file as the
actual directory.  This gives a bit of grace to callers who can use a
selected file as both the default selection and the default directory.


git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1523203 13f79535-47bb-0310-9956-ffa450edef68