travis: verify out-of-tree builds & dist targets

scripts/travis-build.sh

Index: scripts/travis-build.sh
diff --git a/scripts/travis-build.sh b/scripts/travis-build.sh
index 3681f1b5cfaf1654945dc6d760acc954893f9f82..e994fe7b4f003786922aac7f46eed1a51c678651 100755
--- a/scripts/travis-build.sh
+++ b/scripts/travis-build.sh
@@ -19,14 +19,25 @@ setup_env() {
   export JOBS=$(( $NCPUS < 4 ? $NCPUS : 4 ))
 }
 
+# Do an in-tree build and make sure tests pass.
 build() {
   ./configure
   make -j${JOBS} check VERBOSE=1
+  make distclean
+}
+
+# Do an out-of-tree build and make sure we can create a release tarball.
+build_out_of_tree() {
+  mkdir -p build/native
+  cd build/native
+  ../../configure
+  make -j${JOBS} distcheck VERBOSE=1
 }
 
 main() {
   setup_env
   build
+  build_out_of_tree
 }
 
 main "$@"