Remove ipdb dependency

I just found out that ipdb actually uses IPython's own debugger. It only
wraps the set_trace method. Since we don't use set_trace() we can use
IPython.Debugger directly.

bootstrap/requirements.txt

@@ -1,3 +1,2 @@
 nose
 ipython
-ipdb

ipdbplugin.py

@@ -6,7 +6,7 @@
 
 import sys
 import ipdb
-from IPython import ipapi
+import IPython
 from nose.plugins.base import Plugin
 
 class iPdb(Plugin):
@@ -58,8 +58,8 @@ def debug(self, err):
         stdout = sys.stdout
         sys.stdout = sys.__stdout__
         try:
-            ip = ipapi.get()
-            p = ipdb.Pdb(ip.options.colors)
+            ip = IPython.ipapi.get()
+            p = IPython.Debugger.Pdb(ip.options.colors)
             p.reset()
             p.interaction(None, tb)
         finally:

setup.py

@@ -16,7 +16,7 @@
 
     If you have any ideas about how to improve it, come and fork the code at http://github.com/flavioamieiro/nose-ipdb
     """,
-    install_requires=['nose', 'ipython', 'ipdb'],
+    install_requires=['nose', 'ipython'],
     license = 'GNU LGPL',
     keywords = 'test unittest nose nosetests plugin debug ipdb ipython',
     py_modules = ['ipdbplugin'],