ujson fix compile error using clang on Mac OS Lion
I had the compile error below when I built 0.8.0 beta1.  The build was on Mac OS X 10.7.3, using python.org's python version 2.7.3, numpy version 1.6.2, Apple clang version 3.1.

<pre>
clang: pandas/src/ujson/python/JSONtoObj.c
pandas/src/ujson/python/JSONtoObj.c:159:36: error: expression is not assignable
        ((char*)PyArray_DATA(ret)) = new_data;
        ~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
pandas/src/ujson/python/JSONtoObj.c:292:44: error: expression is not assignable
        ((char*)PyArray_DATA(npyarr->ret)) = new_data;
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
</pre>


This patch changes those lines to use PyArray_BYTES instead, so that the assignment is to an lvalue.  The build then succeeds, and nose tests pass.  I also successfully tested on a linux box (Scientific Linux 6.0), running python 2.6.6, numpy 1.6.2, and gcc 4.4.4. (I don't have a windows box to test on)
