The /rewind code is all in the source, but it appears that the opcode still isn't set in the most recent versions of the patch_Titanium.conf file that comes with the Official Downloads.
patch_Titanium.conf
Code:
OP_Rewind=0x4cfa # Lieka: /rewind command
That line needs to be added for the /rewind command to start working. Hopefully this will be in the next source update. But, for the time being, anyone wanting to use it can easily add this line in. It doesn't require a compile, so this can be used with the source or binaries version of the download. It is a simple fix.