largefiles: show also how many data entities are outgoing at "hg summary" Before this patch, "hg summary --large" shows how many largefiles are changed or added in outgoing revisions only in the point of the view of filenames. For example, according to the number of outgoing largefiles shown in "hg summary" output, users should expect that the former below costs much more to upload outgoing largefiles than the latter. - outgoing revisions add a hundred largefiles, but all of them refer the same data entity in this case, only one data entity is outgoing, even though "hg summary" says that a hundred largefiles are outgoing. - a hundred outgoing revisions change only one largefile with distinct data in this case, a hundred data entities are outgoing, even though "hg summary" says that only one largefile is outgoing. But the latter costs much more than the former, in fact. This patch shows also how many data entities are outgoing at "hg summary" by counting number of unique hash values for outgoing largefiles. This patch introduces "_getoutgoings" to centralize the logic (de-duplication, too) into it for convenience of subsequent patches, even though it is not required in "hg summary" case.