Travis: compile qpdf from source

The older version in Travis's Ubuntu 14.04 can't pass the test suite anymore.

.travis.yml

@@ -1,9 +1,9 @@
 dist: trusty
 language: python
 cache:
+  ccache: true
   pip: true
   directories:
-  - packages
   - $HOME/Library/Caches/Homebrew
 
 env:

.travis/linux_before_install.sh

@@ -8,7 +8,6 @@ sudo add-apt-repository ppa:heyarje/libav-11 -y
 sudo apt-get update -qq
 sudo apt-get install -y \
 	ghostscript \
-	qpdf \
 	poppler-utils \
 	libavformat56 \
 	libavcodec56 \
@@ -27,5 +26,17 @@ sudo apt-get install -y --no-install-recommends \
 
 pip install --upgrade pip
 mkdir -p packages
-[ -f packages/unpaper_6.1-1.deb ] || wget -q 'https://www.dropbox.com/s/vaq0kbwi6e6au80/unpaper_6.1-1.deb?raw=1' -O packages/unpaper_6.1-1.deb
+wget -q 'https://www.dropbox.com/s/vaq0kbwi6e6au80/unpaper_6.1-1.deb?raw=1' -O packages/unpaper_6.1-1.deb
 sudo dpkg -i packages/unpaper_6.1-1.deb
+
+if [ ! -f /usr/local/bin/qpdf ]; then
+	export QPDF_RELEASE='https://github.com/qpdf/qpdf/releases/download/release-qpdf-8.0.2/qpdf-8.0.2.tar.gz'
+	mkdir qpdf
+    wget -q $QPDF_RELEASE -O - | tar xz -C qpdf --strip-components=1
+    cd qpdf/
+	export PATH="/usr/local/opt/ccache/libexec:$PATH"
+    ./configure --prefix=/usr
+    make -j 2
+    sudo make install
+    cd ..
+fi

setup.py

@@ -186,7 +186,7 @@ if not forced and command.startswith('install') or \
     )
     check_external_program(
         program='qpdf',
-        need_version='5.1.1',   # limited by Travis CI / Ubuntu 14.04 backports
+        need_version='7.0.0', # test suite known to fail on 5.1.1
         package='qpdf',
         version_check_args=['--version']
     )