infinite loop of failure without report

doc-html errors here lead to infinite failure. Trac ticket was 3021. Update: the failure to recognize and report is however not reproducible with --ticket 3021.

[misc     ] /scratch/sage/src/doc/en/reference/misc/sage/misc/interpreter.rst:: WARNING: document isn't included in any toctree
Error building the documentation.

Note: incremental documentation builds sometimes cause spurious
error messages. To be certain that these are real errors, run
"make doc-clean" first and try again.
Traceback (most recent call last):
  File "/scratch/sage/src/doc/common/builder.py", line 1477, in <module>
    getattr(get_builder(name), type)()
  File "/scratch/sage/src/doc/common/builder.py", line 276, in _wrapper
    getattr(get_builder(document), 'inventory')(*args, **kwds)
  File "/scratch/sage/src/doc/common/builder.py", line 487, in _wrapper
    x.get(99999)
  File "/scratch/sage/local/lib/python/multiprocessing/pool.py", line 554, in get
    raise self._value
OSError: [misc     ] /scratch/sage/src/doc/en/reference/misc/sage/misc/interpreter.rst::    WARNING: document isn't included in any toctree

make: *** [doc-html] Error 1
Traceback (most recent call last):
  File "/scratch/sage/local/bin/patchbot/patchbot.py", line 441, in test_a_ticket
    do_or_die("$MAKE")
  File "/scratch/sage/local/bin/patchbot/util.py", line 91, in do_or_die
    raise exn_class, "%s %s" % (res, cmd)
Exception: 512 $MAKE
Already on 'patchbot/base'
From git://trac.sagemath.org/sage
 + 4e34d0d...7d358ff u/vbraun/build_ecl_with_unicode_enabled ->   patchbot/ticket_upstream  (forced update)
0       2
    Switched to branch 'patchbot/ticket_merged'

sagemath / sage-patchbot

infinite loop of failure without report #20