Support existing guard torrc options better with new guard code, or deprecate them.
These torrc options are guard-related, but I don't know how well the new code supports them (or in some cases, I rather suspect it doesn't).
* UseEntryGuards
* UseEntryGuardsAsDirGuards. (I vote, deprecate this.)
* NumEntryGuards
* NumDirectoryGuards. (I vote, deprecate this.)
* GuardLifetime