git-filesync 0.21.2

Clearer hints for unknown sync points; fewer git calls

Changes:

• The hooks no longer tell to pull a file whose previous sync point isn't
  in the source (pull --all leaves such a file alone); they point to
  status, which explains it.
• The status hint fits the source: a mapped checkout may be behind
  (update it, or use --remote); a cached upstream asks the server, so
  there the commit isn't on the server - history rewritten, synced from an
  unpushed commit or from another upstream - and 'pull FILE' syncs it.
• pull --all names each file it leaves out, with the reason, as
  git-assetsync does: "warning: a.c: missing - left out (see 'git
  filesync status')"; likewise "modified, but not adaptable" and
  "previous sync point not found". Before, only their number was given
  when there were several.
• set --source and source set-url name 'pull FILE' when the synced
  version isn't in the new upstream.
• pull of an adapted file whose synced version is gone upstream names
  'pull --overwrite FILE', which takes the upstream version.
• --overwrite keeps a staged version it replaces also when the working
  tree file is already the upstream version.
• Fewer git calls, which matters most on Windows: short commit ids are
  asked for at once (before, one call each), the first syncs of a pull
  keep discarded content at once, and pull --all reads nothing for files
  it leaves alone. mv of many files stays within the Windows command line
  limit.

Documentation:

• MANUAL: set --source and pull FILE for an unknown sync point; what
  pull --all says about files it leaves out.
• Pinned example versions in README and MANUAL set to v0.21.2.

This release replaces the 0.21.2 of earlier the same day, which gave only
the number of the files pull --all left out.