Merge pull request #274 from tomkooij/hdf5_thread_safe

MRG: Build HDF5 with thread safety enabled

Build HDF5 with --enable-thread-safe flag.

This was brought to my attention by @ZanSara over at pytables/pytables#776

It seems a good idea to enable thread safety for the HDF5 library.

This makes a lot of sense, as the conda-forge [hdf5 package is also build](https://github.com/conda-forge/hdf5-feedstock/blob/master/recipe/build.sh) with this flag.

library_builders.sh

@@ -227,7 +227,7 @@ function build_hdf5 {
     local short=$(echo $HDF5_VERSION | awk -F "." '{printf "%d.%d", $1, $2}')
     fetch_unpack $hdf5_url/hdf5-$short/hdf5-$HDF5_VERSION/src/hdf5-$HDF5_VERSION.tar.gz
     (cd hdf5-$HDF5_VERSION \
-        && ./configure --with-szlib=$BUILD_PREFIX --prefix=$BUILD_PREFIX \
+        && ./configure --with-szlib=$BUILD_PREFIX --prefix=$BUILD_PREFIX --enable-thread-safe \
         && make -j4 \
         && make install)
     touch hdf5-stamp