add support for RPM %define lines in the spec file

Added support for %define lines in the RPM spec file. To use them, 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>