outgoing: introduce "outgoinghooks" to avoid redundant outgoing check This patch introduces "outgoinghooks" to avoid redundant outgoing check for "hg outgoing" in other than "commands.outgoing" (or utility functions used by it).

hg: make "_outgoing()" return peer object for remote repository This patch makes "_outgoing()" return peer object for remote repository, to avoid re-execution "expandpath()", "parseurl()", and "peer()" on caller side for specified URL.

hg: make "_outgoing()" return empty list instead of "None" This patch makes "_outgoing()" return empty list instead of "None", if there are no outgoing changesets, because: - returning "None" requires callers to examine whether returned value is "None" or not explicitly, if callers want to execute loop on returned value, but - there are no explicit needs to return "None"

largefiles: use "summaryremotehooks" to avoid redundant outgoing check Before this patch, "hg summary --remote --large" invokes "findcommonoutgoing()" not only in "commands.summary()" but also in "overrides.overridesummary()" (via "getoutgoinglfiles()"). The latter is redundant. This patch uses "summaryremotehooks" to avoid redundant outgoing check. Newly introduced function "overrides.summaryremotehook()" is registered into "summaryremotehooks" to get the result of outgoing check in "commands.summary()". It invokes "lfutil.getlfilestoupload()" directly with the result of outgoing check to avoid redundant outgoing check in "getoutgoinglfiles()".