don't cleanup cdrom files in apt-get update

Regression from merging 801745284905e7962aa77a9f37a6b4e7fcdc19d0 and
b0f4b486e6850c5f98520ccf19da71d0ed748ae4. While fine by itself, merged
the part fixing the filename is skipped if a cdrom source is
encountered, so that our list-cleanup removes what seems to be orphaned
files.

Closes: 765458
Merge branch 'debian/sid' into debian/experimental

The acquire code changed completely, so this is more an import of the
testcase and a new fix than the merge of an existent fix.

Conflicts:
	apt-pkg/acquire-item.cc
ignore Acquire::GzipIndexes for cdrom sources

We do not support compressed indexes for cdrom sources as we rewrite
some of them, so supporting it correctly could be hard. What we do
instead in the meantime is probably disabling it for cdrom sources.
releasing package apt version 1.1~exp7