Add travis-lint script

This uses $TRAVIS_BRANCH to find the pull-request merge target,
and installs the needed Python package.

Author: smowton

.travis.yml

@@ -40,7 +40,7 @@ matrix:
       compiler: clang
       env: COMPILER=clang++
     - env: NAME="CPP-LINT"
-      script: scripts/run_lint.sh master HEAD || true
+      script: scripts/travis_lint.sh || true
 
 script:
   - if [ -L bin/gcc ] ; then export PATH=$PWD/bin:$PATH ; fi ;

scripts/travis_lint.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+set -e
+
+script_folder=`dirname $0`
+pip install --user unidiff
+
+if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
+  $script_folder/run_lint.sh HEAD~1 # Check for errors introduced in last commit
+else
+  $script_folder/run_lint.sh $TRAVIS_BRANCH # Check for errors compared to merge target
+fi
+