Re-enable continuation prompts

Now that prompt_toolkit 0.58 is out, this should work.

IPython/terminal/ptshell.py

@@ -154,9 +154,7 b' class TerminalInteractiveShell(InteractiveShell):'
         app = create_prompt_application(multiline=True,
                             lexer=PygmentsLexer(Python3Lexer if PY3 else PythonLexer),
                             get_prompt_tokens=self.get_prompt_tokens,
-                            # The line below is waiting for a new release of
-                            # prompt_toolkit (> 0.57)
-                            #get_continuation_tokens=self.get_continuation_tokens,
+                            get_continuation_tokens=self.get_continuation_tokens,
                             key_bindings_registry=kbmanager.registry,
                             history=history,
                             completer=IPythonPTCompleter(self.Completer),

setup.py

@@ -195,7 +195,7 b' install_requires = ['
     'pickleshare',
     'simplegeneric>0.8',
     'traitlets',
-    'prompt_toolkit',  # We will require > 0.57 once a new release is made
+    'prompt_toolkit>=0.58',
 ]
 
 # Platform-specific dependencies: