GUB dblatex breaks compile

[Graham Percival]

GUB cannot build master:


lilypond-book.py (GNU LilyPond) 2.15.30
cd ./out-test && dblatex suffix-lyxml.xml
Traceback (most recent call last):
  File "/usr/bin/dblatex", line 10, in ?
    from contrib.debian.errorhandler import DebianHandler
  File "/usr/share/dblatex/lib/contrib/debian/errorhandler.py",
line 8, in ?
    import apt
ImportError: No module named apt
make[1]: *** [out-test/suffix-lyxml.pdf] Error 1
make[1]: Leaving directory
`/main/src/gub/target/linux-x86/build/lilypond-git.sv.gnu.org--lilypond.git-release-unstable/input/regression/lilypond-book'
make: *** [test] Error 2



Julien, the lilypond-book regtests are the obvious contender for
this.  If the bugfix is not obvious, could you revert that commit
so that we can have the 2.15.30 release while we investigate this
as a separate patch?

The correct bugfix may be simply to update the version of dblatex
in GUB, but that is rarely as simple as it sounds.

- Graham