Change in LOCAL HDF ftp server

Please be aware that the URL of the *LOCAL* HDF Group ftp server will be permanently changing to:

    https://gamma.hdfgroup.org/ftp/

Previously, files could be obtained by using either the above address or:

    ftp://ftp.hdfgroup.uiuc.edu/

This change should NOT affect most users. The local ftp server is only used as a
temporary means for obtaining snapshots and other files that are not part of the
standard released software.