gwyddion: Update to version 2.28

[feranick@…]

Currently gwyddion is in version 2.26 in macports. version 2.27 was staged in a separate bug report, but it never made to the stable repository. Now version 2.28 (with some important support for additional file formats) is available upstream and it would be great to have it on macports.

Changelog:
    Nanoscantech (new): Imports NanoScanTech .nstdat files.
    TIA SER (new): Imports FEI Tecnai imaging and analysis .ser files.
    DM3 (new): Imports Digital Micrograph DM3 TEM images (only greyscale data at present).
    PID (new): Simple simulation of PID loop effects during scanning.
    Lateral force (new): Simulation of lateral force from topography channel.
    Neural network (new): Neural network data processing.
    XY denoise (new): Data denoising based on horizontal and vertical scans.
    WIP: Spectral transformation for Raman data was fixed and swapped XY axes in datafields were really fixed.
    Zeiss: Files without key-value pairs in tag 34118 are recognised and loaded.

Other

    Compatibility with libpng 1.5 was corrected.
    GNOME 3 thumbnailer file is installed, making gwyddion-thumbnailer work automatically in GNOME 3.
    configure has an option --enable-home-installation to ease desktop integration if you compile from source code and install to your home.

[ryandesign (Ryan Carsten Schmidt)]

I did not find a separate ticket for 2.27.