RF: Add back the optional import machinery in each one of these, so that

individual imports are also handled.

dipy/viz/_show_odfs.py

@@ -1,10 +1,16 @@
 import numpy as np
 
-# Mayavi appears in many guises:
-try:
-    from enthought.mayavi import mlab
+try: 
+    # Mayavi appears in many guises:
+    try:
+        from enthought.mayavi import mlab
+    except ImportError:
+        from mayavi import mlab
+# But if you don't have it, we're not going to give you too much of a hard time:
 except ImportError:
-    from mayavi import mlab
+    e_s = "You do not have Mayavi installed. Some visualization functions"
+    e_s += " might not work."
+    print(e_s)
 
 from dipy.utils.spheremakers import sphere_vf_from
 

dipy/viz/projections.py

@@ -8,9 +8,14 @@
 import numpy as np
 import scipy.interpolate as interp
 
-import matplotlib
-import matplotlib.pyplot as plt
-import matplotlib.tri as tri
+try:
+    import matplotlib
+    import matplotlib.pyplot as plt
+    import matplotlib.tri as tri
+except ImportError:
+    e_s = "You do not have Matplotlib installed. Some visualization functions"
+    e_s += " might not work for you."
+    print(e_s)
 
 import dipy.core.geometry as geo