[mod_webdav] map COPY/MOVE Destination to aliases (fixes #1787)
attempt to remap COPY/MOVE Destination to aliased physical paths
by finding common URI prefix between request URI and Destination
and finding how that part of the request URI was mapped to a
physical path.
This will work if the aliased physical path is above the webdav root.
It is not a good idea to remap physical paths within a webdav root.
Note: webdav paths and webdav properties are managed by mod_webdav,
so do not modify paths externally or else undefined behavior
or corruption may occur
x-ref:
"Bug in mod_webdav when using aliases and MOVE command"
https://redmine.lighttpd.net/issues/1787