Only run tests that require muparser if we have indeed configured with muparser.

diff --git a/tests/manifold/function_manifold_01.output b/tests/manifold/function_manifold_01.with_muparser=true.output
similarity index 100%
rename from tests/manifold/function_manifold_01.output
rename to tests/manifold/function_manifold_01.with_muparser=true.output

diff --git a/tests/manifold/function_manifold_02.output b/tests/manifold/function_manifold_02.with_muparser=true.output
similarity index 100%
rename from tests/manifold/function_manifold_02.output
rename to tests/manifold/function_manifold_02.with_muparser=true.output