BUG: Scrolling pager in vsplit on Mac OSX tears.
BUG: Scrolling pager in vsplit on Mac OSX tears.

On Mac OS X, scrolling the pager when it is split vertically causes the
help text to tear (i.e. the help text is unreadable).  This hack
attempts to make it a little better although the solution may not be
optimal at all.

ipython/ipython,ipython/ipython