Merge branch 'ps/pseudo-refs'

Assorted changes around pseudoref handling.

* ps/pseudo-refs:
  bisect: consistently write BISECT_EXPECTED_REV via the refdb
  refs: complete list of special refs
  refs: propagate errno when reading special refs fails
  wt-status: read HEAD and ORIG_HEAD via the refdb

diff --cc builtin/bisect.c
Simple merge

diff --cc refs.c
Simple merge

diff --cc t/t1403-show-ref.sh
Simple merge

diff --cc t/t6030-bisect-porcelain.sh
Simple merge

diff --cc wt-status.c
Simple merge