Pinned dependencies

Please note: currently the latest pinnings are in pin_the_slow_way.py.

In order to maintain a freely installable collection of built distributions, we currently attempt to provide builds against the following dependency versions:

          'boost': 'boost 1.61.*',
          'bzip2': 'bzip2 1.0.*',
          'ffmpeg': 'ffmpeg 2.8.*',
          'fontconfig': 'fontconfig 2.11.*',
          'freetype': 'freetype 2.6.*',
          'geos: geos 3.4.*',
          'hdf5': 'hdf5 1.8.17|1.8.17.*',
          'icu': 'icu 56.*',
          'jpeg': 'jpeg 9*',
          'libblitz': 'libblitz 0.10|0.10.*',
          'libmatio': 'libmatio 1.5.*',
          'libnetcdf': 'libnetcdf 4.4.*',
          'libpng': 'libpng >=1.6.21,<1.7',
          'libsvm': 'libsvm 3.21|3.21.*',
          'libtiff': 'libtiff 4.0.*',
          'ncurses': 'ncurses 5.9*',
          'openssl': 'openssl 1.0.*',
          'readline': 'readline 6.2*',
          'sox': 'sox 14.4.2',
          'sqlite': 'sqlite 3.13.*',
          'tk': 'tk 8.5.*',
          'vlfeat': 'vlfeat 0.9.20',
          'xz': 'xz 5.2.*',
          'zlib': 'zlib 1.2.*',