Added missing bob.sp import

As discussed here:
https://groups.google.com/forum/?fromgroups#!topic/bob-devel/W8Cy-8tamGM

bob/learn/em/__init__.py

@@ -2,6 +2,7 @@
 import bob.io.base
 import bob.math
 import bob.learn.linear
+import bob.sp
 
 # import our own Library
 import bob.extension