tests/test-hgk.t

largefiles: centralize the logic to get outgoing largefiles

Before this patch, "overrides.getoutgoinglfiles()" (called by
"overrideoutgoing()" and "overridesummary()") and "lfilesrepo.push()"
implement similar logic to get outgoing largefiles separately.

This patch centralizes the logic to get outgoing largefiles in
"lfutil.getlfilestoupload()".

"lfutil.getlfilestoupload()" takes "addfunc" argument, because each
callers need different information (and it is useful for enhancement
in the future).

  - "overrides.getoutgoinglfiles()" needs only filenames
  - "lfilesrepo.push()" needs only hashes of largefiles

Minimal hgk check

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "hgk=" >> $HGRCPATH
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debug-cat-file commit 0
  tree a0c8bcbbb45c
  parent 000000000000
  author test 0 0
  revision 0
  branch default
  phase draft
  
  adda

  $ cd ..