Avoid justifying of 'in' prompt

This little diff is to avoid rjustify of the 'in' prompt, because in configurations with variable prompt size (e.g. my pysh prompt showing \w), going to a smaller prompt cause only-reversed-by-restart blank spaces addition in beggining of 'in' prompt. Right justify is ok to 'in2' and 'out' prompts, but very ugly and weird in 'in' prompt.

IPython/core/prompts.py

@@ -423,7 +423,7 b' class PromptManager(Configurable):'
         self.txtwidth = _lenlastline(res) - invis_chars
         just = self.justify if (just is None) else just
         # If the prompt spans more than one line, don't try to justify it:
-        if just and ('\n' not in res) and ('\r' not in res):
+        if just and name != 'in' and ('\n' not in res) and ('\r' not in res):
             res = res.rjust(self.width + invis_chars)
         self.width = _lenlastline(res) - invis_chars
         return res