RPM %define support attempt

I can't claim I fully know what I'm doing, but some hacking on the code resulted in what appears to not break things, as the tests pass Let me know your thoughts?

To use the %define support, add in a defineStatements tag with define tags specifying the values to use for %define lines:
```
<configuration>
  <rpm>
    <defineStatements>
      <define>_source_filedigest_algorithm md5</define>
      <define>_binary_filedigest_algorithm md5</define>
      <define>_source_payload w9.gzdio</define>
      <define>_binary_payload w9.gzdio</define>
    </defineStatements>
...
</configuration>
```