[Crash-utility] Fix buildrequires in RPM spec file to build sial extention.

Gday, I noticed that the documentation on the extention page ( http://people.redhat.com/anderson/extensions.html ) mentions that the sial scripts should be built by default when crash is built. In the current release (version 6.0.0) the sial scripts are not being built due to a missing BuildRequires dependencies in the spec file, in my case specifically flex and bison. Attached is a modification to the crash.spec file to include the correct BuildRequires. Thanks, Wade Mealing