Removed --libpath long name.

IPython/extensions/cythonmagic.py

@@ -125,7 +125,7 b' class CythonMagics(Magics):'
              "multiple times)."
     )
     @magic_arguments.argument(
-        '-L', '--libpath', action='append', default=[],
+        '-L', dest='library_dirs', metavar='dir', action='append', default=[],
         help="Add a path to the list of libary directories (can be specified "
              "multiple times)."
     )
@@ -200,7 +200,7 b' class CythonMagics(Magics):'
                 name = module_name,
                 sources = [pyx_file],
                 include_dirs = c_include_dirs,
-                library_dirs = args.libpath,
+                library_dirs = args.library_dirs,
                 extra_compile_args = args.compile_args,
                 extra_link_args = args.link_args,
                 libraries = args.lib,