Merge branches 'gf/ls', 'gf/tag', 'zz/import-rsnapshot' and 'bl/selfindex'

Merge branches 'gf/ls', 'gf/tag', 'zz/import-rsnapshot' and 'bl/selfindex'

* gf/ls:
  ls-cmd: hide files with a leading dot by default

* gf/tag:
  Refuse branch/tag names that start with a dot
  tag-cmd: Some fixups

* zz/import-rsnapshot:
  Adds a testcase for import-rsnapshot.
  Makes import-rsnapshot use save's -f option.
  Adds -f option to save to use a given indexfile.
  Makefile: handle shell commands (cmd/*-cmd.sh)
  Adds documentation for bup-import-rsnapshot
  Adds import-rsnapshot command.
  Adds documentation for save's strip option.
  Adds testcases for --strip and --strip-path.
  Adds a strip and strip-path option to bup save.

* bl/selfindex:
  Rename receive-objects command to receive-objects-v2.
  Write idxs directly rather than using git-index-pack.
  Send SHAs from the client to reduce server load
  Use chunkyreader() instead of manually reading multiple blocks.