Merge commits can include novel changes not present in any parent, and
should be scanned. The git log command with -p shows merge commits,
commits but without any diffs, so we were not scanning that content.
The "low memory" mode does get merge diffs in git show, but they're in a
format the parser isn't prepared to handle, and changes would need
careful testing.
There are a few ways to show the merge diffs, some make it easier to
show any novel changes, but require some parser/test adjustment or
version checks. "first-parent" is the simplest "what did this merge
introduce" diff, meaning we double scan content from other parents, but
also include changes that are only in the merge.
Meredith Howard
295d2f3760