Merge branch 'jk/trace-fixup'

Various small fixups to the "GIT_TRACE" facility. * jk/trace-fixup: trace: do not fall back to stderr write_or_die: drop write_or_whine_pipe() trace: disable key after write error trace: correct variable name in write() error message trace: cosmetic fixes for error messages trace: use warning() for printing trace errors trace: stop using write_or_whine_pipe() trace: handle NULL argument in trace_disable()