Unfortunately a glob like osmo-x__*.{svg,png} doesn't work, so have the
suffixes in separate globs.
Add dashes to indicate that failure should be ignored.
Change-Id: I6bc4d9ea72b43a573acbc860c23397f748de2c7b
The manuals existed in different form for several years in an internal
sysmocom repository. However, since they had just recently been
converted from docboox-xml to asciidoc and all files have been
re-shuffled for enabling the public release, there's not much point in
keeping the history with git-filter-branch.