Merge branch 'jx/sideband-cleanup'

Merge branch 'jx/sideband-cleanup'

The side-band demultiplexer that is used to display progress output
from the remote end did not clear the line properly when the end of
line hits at a packet boundary, which has been corrected.  Also
comes with test clean-ups.

* jx/sideband-cleanup:
  test: refactor to use "get_abbrev_oid" to get abbrev oid
  test: refactor to use "test_commit" to create commits
  test: compare raw output, not mangle tabs and spaces
  sideband: don't lose clear-to-eol at packet boundary