We had some call sites that inspected flags on a repository's SCMTool,

in order to handle some logic or relay capabilities elsewhere. Some of

these call sites were fetching the tool directly, in some cases

instantiating it, and then accessing the flags. For instance, there were

many blocks of code accessing SCMTool.diffs_use_absolute_paths

inefficiently.
We already had wrappers in Repository for accessing some of these

flags, which was more efficient. These looked up by class when possible,

instantiating only if necessary. In other cases, the flags could be

looked up on the class, rather than needing an instance.
This change updates all references to use the wrappers in the

Repository. It also makes the Repository.diffs_use_absolute_paths

wrapper properly a cached_property, to avoid repeated lookups and

instantiations.

Unit tests pass.