[Fractint] Update 2021-03-07 to SDL version

Folks, Fixed location of zoom box created with the mouse when renderer or window are not sized to sxdots and sydots. Speed up for saving and restoring images. Look in the directory at: https://www.fractint.net/ftp/experimental/ For: Windows version (32-bit) is: SDL2-fractint-20.05alpha-2021-03-07.zip Pre-compiled 64-bit Linux version is: SDL2-Xfractint-20.05alpha-2021-03-07.tar.xz Note that Tim's mirror site at fractint.org has not been updated. Jonathan