qtconsole: wrap argument list in tooltip to match width of text body

previously, a function with a long argument list would produce
a very wide tooltip, hurting readability.

Since the width of the docstring body is chosen by the developer
whereas the formatting of the argument list is currently not, it's
reasonable to wrap the argument list width to the maximum of
a) 80 characters, or b) maximum length of a line in the docstring body.

This improved readability, without unduly affecting the appearence
of the docstring body itself.

closes  #2661

IPython/frontend/qt/console/call_tip_widget.py

@@ -137,7 +137,7 b' class CallTipWidget(QtGui.QLabel):'
 
         if call_line:
             doc = '\n\n'.join([call_line, doc])
-        return self.show_tip(doc)
+        return self.show_tip(self._format_tooltip(doc))
 
     def show_tip(self, tip):
         """ Attempts to show the specified tip at the current cursor location.
@@ -248,6 +248,17 b' class CallTipWidget(QtGui.QLabel):'
             QtGui.qApp.topLevelAt(QtGui.QCursor.pos()) != self):
             self._hide_timer.start(300, self)
 
+    def _format_tooltip(self,doc):
+        import textwrap
+
+        # make sure a long argument list does not make
+        # the first row overflow the width of the actual tip body
+        rows = doc.split("\n")
+        max_text_width = max(80, max([len(x) for x in rows[1:]]))
+        rows= textwrap.wrap(rows[0],max_text_width) + rows[1:]
+        doc = "\n".join(rows)
+        return doc
+
     #------ Signal handlers ----------------------------------------------------
 
     def _cursor_position_changed(self):