zsh_completion: make use of `debuglabelcomplete` command
Use `debuglabelcomplete` command when populating labels list, instead of
calling `hg` three times: for branches, bookmarks and tags. Do not pass string
being completed to `hg debuglabelcomplete` (as `$words[$CURRENT]`), since it
breaks `_hg_revrange` completion (`--rev 2.5:2.5.<Tab>`) for no apparent
benefit.
Also complete `hg view` with labels, not just tags, and drop unused `_hg_tags`.
$ hg init
$ echo a > a
$ hg add a
$ hg commit -m test
Do we ever miss a sub-second change?:
$ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do
> hg co -qC 0
> echo b > a
> hg st
> done
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a
M a