When loading a template in scan mode, let preprocess know it only needs to scan.

When loading a template in scan mode, let preprocess know it only needs to scan.

This makes wikis such as zack's much faster in the scan pass.
In that pass, when a template contains an inline, there is no reason to
process the entire inline and all its pages. I'd forgotten to pass
along the flag to let preprocess() know it was in scan mode, leading to
much unncessary churning.