Read SCCACHE_RECACHE from the client
Read SCCACHE_RECACHE from the client

Now that client env vars are sent to the server, this was much easier! This
allows forcing a recache from the client rather than having to set it for the
entire server.

Closes #96

mozilla/sccache,glandium/sccache,glandium/sccache,glandium/sccache,luser/sccache2,mozilla/sccache,mozilla/sccache,luser/sccache2,luser/sccache2,glandium/sccache,luser/sccache2