fix an incompatibility with virtualenv (rhbz#742641)
    
    Previously, we manually fixed up the library search path to be
    below %{pypyprefix}, by patching pypy/translator/goal/app_main.py (adding
    LIBRARY_INSTALLATION_PATH in patch 3, then using sed to change it to the
    correct value in %prep after applying the patch).
    
    This led to issues when using pypy with virtualenv, so now (as suggested in
    https://codespeak.net/issue/pypy-dev/issue614 ) we simply install the pypy
    binary into %{pypyprefix}, and make /usr/bin/pypy be a symlink to it.  This
    allows pypy to find its libraries both when run outside a virtualenv, and
    within it.
    
    Resolves https://bugzilla.redhat.com/show_bug.cgi?id=742641