Build: Enable valgrind's --leak-check when testing the API

.valgrind.supp

@@ -5,3 +5,28 @@
    fun:nss_parse_service_list
    fun:__nss_database_lookup
 }
+{
+   ex_function_1
+   Memcheck:Leak
+   fun:malloc
+   fun:try_malloc
+   fun:xmalloc
+   fun:ex_function
+}
+{
+   ex_function_2
+   Memcheck:Leak
+   fun:realloc
+   fun:xrealloc
+   fun:ga_grow
+   fun:ex_function
+}
+{
+   ex_function_3
+   Memcheck:Leak
+   fun:malloc
+   fun:strdup
+   fun:xstrdup
+   fun:vim_strsave
+   fun:ex_function
+}

scripts/travis.sh

@@ -3,6 +3,7 @@
 tmpdir="$(pwd)/tmp"
 rm -rf "$tmpdir"
 mkdir -p "$tmpdir"
+suppressions="$(pwd)/.valgrind.supp"
 
 valgrind_check() {
 	(
@@ -171,7 +172,7 @@ elif [ "$TRAVIS_BUILD_TYPE" = "api/python" ]; then
   sudo pip install .
   sudo pip install nose
 	test_cmd="nosetests --verbosity=2"
-	nvim_cmd="valgrind -q --track-origins=yes --log-file=$tmpdir/valgrind-%p.log ../build/bin/nvim -u NONE"
+	nvim_cmd="valgrind -q --track-origins=yes --leak-check=yes --suppressions=$suppressions --log-file=$tmpdir/valgrind-%p.log ../build/bin/nvim -u NONE"
 	if ! ../scripts/run-api-tests.exp "$test_cmd" "$nvim_cmd"; then
 		valgrind_check "$tmpdir"
 		exit 1