Build hdf5 with szlib on Travis CI

As reported by #59

.install_hdf5_1_8.sh

@@ -1,6 +1,12 @@
 #! /bin/sh 
 
-git clone --branch hdf5_1_8_18 https://bitbucket.hdfgroup.org/scm/hdffv/hdf5.git hdf5_1_8_18
+curl https://support.hdfgroup.org/ftp/lib-external/szip/2.1.1/src/szip-2.1.1.tar.gz -O -J
+tar -zxf szip-2.1.1.tar.gz
+cd szip-2.1.1
+./configure --quiet --enable-static=no CFLAGS="-w"
+make install -C src
+cd ..
+git clone --quiet --depth 1 --branch hdf5_1_8_18 https://bitbucket.hdfgroup.org/scm/hdffv/hdf5.git hdf5_1_8_18
 cd hdf5_1_8_18
-./configure --quiet --enable-shared --disable-production --enable-debug=all --with-pic --disable-deprecated-symbols --disable-hl --disable-strict-format-checks --disable-clear-file-buffers --disable-instrument --disable-parallel --disable-trace --with-default-api-version=v18 CFLAGS="-w"
+./configure --enable-shared --disable-production --enable-debug=all --with-pic --disable-deprecated-symbols --disable-hl --disable-strict-format-checks --disable-clear-file-buffers --disable-instrument --disable-parallel --disable-trace --with-default-api-version=v18 --with-szlib=$TRAVIS_BUILD_DIR/szip-2.1.1/szip CFLAGS="-w"
 make install -C src

.travis.yml

@@ -137,7 +137,7 @@ install:
 
 before_script:
   - ./autogen.sh
-  - ./configure --quiet --enable-shared --enable-coverage --enable-debug --enable-mat73=$ENABLE_MAT73 --enable-extended-sparse=$ENABLE_EXTENDED_SPARSE --with-zlib=$WITH_ZLIB --with-pic --with-hdf5=$TRAVIS_BUILD_DIR/$HDF5_VERSION_DIR/hdf5
+  - ./configure --enable-shared --enable-coverage --enable-debug --enable-mat73=$ENABLE_MAT73 --enable-extended-sparse=$ENABLE_EXTENDED_SPARSE --with-zlib=$WITH_ZLIB --with-pic --with-hdf5=$TRAVIS_BUILD_DIR/$HDF5_VERSION_DIR/hdf5
 
 script:
   - if [[ "$COVERITY_SCAN_BRANCH" != 1 ]]; then make; fi