Put source mods for the siac library in this directory.

WARNING: SourceMods are not kept under version control, and can easily
become out of date if changes are made to the source code on which they
are based. We only recommend using SourceMods for small, short-term
changes that just apply to one or two cases. For larger or longer-term
changes, including gradual, incremental changes towards a final
solution, we highly recommend making changes in the main source tree,
leveraging version control (git or svn).
