Add script to build doxygen

Move the section in .travis.yml responsible for getting the latest
version of doxygen to a separate script, in order to make it easier
for Ubuntu users to install it locally.

Author: John Nonweiler

.travis.yml

@@ -63,10 +63,7 @@ jobs:
           # Build doxygen if it is not in Travis cache
           if ! [ -x doxygen/build/bin/doxygen ]
           then
-            mkdir -p doxygen/build \
-            && wget http://ftp.stack.nl/pub/users/dimitri/doxygen-${DOXYGEN_VERSION}.src.tar.gz -O- | tar -xz --strip-components=1 --directory doxygen \
-            && ( cd doxygen/build && cmake .. ) \
-            && make -j4 -C doxygen/build
+            scripts/build_doxygen.sh ${DOXYGEN_VERSION}
           fi
         - export PATH="$PATH:${TRAVIS_BUILD_DIR}/doxygen/build/bin"
       script:

scripts/build_doxygen.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+DOXYGEN_VERSION=$1
+
+if [ $# -ne 1 ]
+then
+  echo "Usage: build_doxygen.sh doxygen-version-number"
+  exit 1
+fi
+
+mkdir -p doxygen/build \
+&& wget http://ftp.stack.nl/pub/users/dimitri/doxygen-${DOXYGEN_VERSION}.src.tar.gz -O- | tar -xz --strip-components=1 --directory doxygen \
+&& ( cd doxygen/build && cmake .. ) \
+&& make -j4 -C doxygen/build