lybook-db and make xxx-clean

[Joe Neeman]

It seems that some changes in the way lilypond-books output is stored have broken certain build rules, particularly ones that clean stuff. For example,

$ make check
$ make test-clean
$ time make check
real    0m31.410s
user    0m25.598s
sys    0m4.084s
$ make test-clean && rm -fr out/lybook-db
$ time make check
real    6m42.076s
user    6m18.948s
sys    0m14.981s

Since the first build time is so short, it seems that 'make test-clean' is not correctly cleaning everything. I think there is a similar problem with make web-clean, but I haven't investigated thoroughly because 'make web' takes so long anyway.

Also, 'make check' prints an informative message:
For tracking crashes: use

    grep sourcefilename `grep -L systems.texi input/regression/out-test/*log|sed s/log/ly/g`

but the command given no longer works because the files no longer go in input/regression/out-test.

Joe