problems with lilypond book after upgrading to 2.2.2

[Ben Crowell]

Once the process has hung up for a long time, if I hit control-C,
I get a whole bunch of output, which was apparently waiting to be
flushed. The tail end of the output contains the following python
stack trace:

[...lots of output...]
paper output to `lily-1813701034.tex'...

Traceback (most recent call last):
  File "/usr/local/bin/lilypond-book", line 1042, in ?
    main ()
  File "/usr/local/bin/lilypond-book", line 1039, in main
    do_file (files[0])
  File "/usr/local/bin/lilypond-book", line 958, in do_file
    process_snippets (process_cmd, outdated)
  File "/usr/local/bin/lilypond-book", line 793, in process_snippets
    ly.system (string.join ([cmd] + names))
  File "/usr/local/share/lilypond/2.2.2/python/lilylib.py", line 332, in system
    sys.stderr.write (open (error_log_file).read ())
KeyboardInterrupt