Test case for issue 96, replicating cgmath AsMut ambiguity.

issue96.patch

diff --git a/imgui-examples/examples/test_window_impl.rs b/imgui-examples/examples/test_window_impl.rs
index c9cc5c8..e5ec03a 100644
--- a/imgui-examples/examples/test_window_impl.rs
+++ b/imgui-examples/examples/test_window_impl.rs
@@ -4,9 +4,34 @@ extern crate imgui;
 extern crate imgui_glium_renderer;
 
 use imgui::*;
+use std::mem;
 
 mod support;
 
+struct Vector3 {
+  x: f32, y: f32, z: f32,
+}
+
+impl From<[f32; 3]> for Vector3 {
+  fn from(v: [f32; 3]) -> Self {
+    Self {
+      x: v[0], y: v[1], z: v[2]
+    }
+  }
+}
+
+impl AsMut<[f32; 3]> for Vector3 {
+  fn as_mut(&mut self) -> &mut [f32; 3] {
+    unsafe { mem::transmute(self) }
+  }
+}
+
+impl AsMut<(f32, f32, f32)> for Vector3 {
+  fn as_mut(&mut self) -> &mut (f32, f32, f32) {
+    unsafe { mem::transmute(self) }
+  }
+}
+
 struct State {
     show_app_main_menu_bar: bool,
     show_app_console: bool,
@@ -40,7 +65,7 @@ struct State {
     vec3f: [f32; 3],
     vec2i: [i32; 2],
     vec3i: [i32; 3],
-    col1: [f32; 3],
+    col1: Vector3,
     col2: [f32; 4],
     selected_fish: Option<usize>,
     auto_resize_state: AutoResizeState,
@@ -88,7 +113,7 @@ impl Default for State {
             vec3f: [0.10, 0.20, 0.30],
             vec2i: [10, 20],
             vec3i: [10, 20, 30],
-            col1: [1.0, 0.0, 0.2],
+            col1: Vector3::from([1.0, 0.0, 0.2]),
             col2: [0.4, 0.7, 0.0, 0.5],
             selected_fish: None,
             auto_resize_state: Default::default(),
@@ -430,7 +455,7 @@ fn show_test_window(ui: &Ui, state: &mut State, opened: &mut bool) {
                     .build();
                 ui.input_float3(im_str!("input float3"), &mut state.vec3f)
                     .build();
-                ui.color_edit(im_str!("color 1"), &mut state.col1).build();
+                ui.color_edit(im_str!("color 1"), state.col1.as_mut()).build();
                 ui.color_edit(im_str!("color 2"), &mut state.col2).build();
 
                 ui.tree_node(im_str!("Multi-component Widgets")).build(|| {