Workaround for travis performing shallow clones with wrong branch

travis clones a repo by 'git clone --depth 50 repo' which is ok if the
PR target is the master branch.  It should actually add '--branch=
$TRAVIS_BRANCH' to the clone command.  This commit provides a
workaround.

Amendment from upstream commit: removed --unshallow, which git rejects for this repository for unknown reasons.

Author: peterschrammel

scripts/travis_doxygen.sh

@@ -8,5 +8,9 @@ pip install --user unidiff
 if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
   $script_folder/run_diff.sh DOXYGEN HEAD~1 # Check for errors introduced in last commit
 else
-  $script_folder/run_diff.sh DOXYGEN $TRAVIS_BRANCH # Check for errors compared to merge target
+  TMP_HEAD=$(git rev-parse HEAD)
+  git config remote.origin.fetch +refs/heads/$TRAVIS_BRANCH:refs/remotes/origin/$TRAVIS_BRANCH
+  git fetch
+  git checkout $TMP_HEAD
+  $script_folder/run_diff.sh DOXYGEN origin/$TRAVIS_BRANCH # Check for errors compared to merge target
 fi

scripts/travis_lint.sh

@@ -8,5 +8,9 @@ pip install --user unidiff
 if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
   $script_folder/run_diff.sh CPPLINT HEAD~1 # Check for errors introduced in last commit
 else
-  $script_folder/run_diff.sh CPPLINT $TRAVIS_BRANCH # Check for errors compared to merge target
+  TMP_HEAD=$(git rev-parse HEAD)
+  git config remote.origin.fetch +refs/heads/$TRAVIS_BRANCH:refs/remotes/origin/$TRAVIS_BRANCH
+  git fetch
+  git checkout $TMP_HEAD
+  $script_folder/run_diff.sh CPPLINT origin/$TRAVIS_BRANCH # Check for errors compared to merge target
 fi