rebase: fix --collapse with --keepbranches (issue2100)
This was broken in 38fe86fb16e3.
Basic install: $ make # see install targets $ make install # do a system-wide install $ hg debuginstall # sanity-check setup $ hg # see helpSee http://mercurial.selenic.com/ for detailed installationinstructions, platform-specific notes, and Mercurial user information.