Update config.guess, zlib, png, jpeg, gettext, glib, pixman, libxml
Explicitly link libgcc statically

gcc 4.8 now links libgcc dynamically by default.  Shared libgcc is
clearly preferable, and in fact is strongly recommended by the gcc
documentation, but does not appear to qualify for the GCC Runtime
Library Exception.  Force continued use of static libgcc.  libtool
filters the relevant option out of LDFLAGS, so force is, in fact,
required.
Rename README.markdown to README.md
Recompress gzipped source tarballs in sdist

Using xz compression for all sources saves ~18 MB in the winbuild zip.
Disable Automake dependency tracking

We don't need it, and the documentation claims that disabling it can
improve performance.
Disable libtiff error dialog boxes

The default libtiff error handlers on Windows will display a dialog box,
which is almost certainly not the desired behavior.  Disable this in
favor of printing a message to stderr, which is the default on Unix.

http://lists.andrew.cmu.edu/pipermail/openslide-users/2013-July/000630.html
Fix 64-bit glib build