svn checkout a single file

When you do this with cvs, you get the directory the file belongs to,
but only containing this file.  A subsequent 'cvs update' will pull in
the rest of the directory.  I'm not sure whether svn should mimic that
behavior or not, just documenting it.

For export, it may be a good idea not to bother with the containing
directory, and instead just spit out the requested file.

Original issue reported by epg