mandoc provides several files that were so far shippped with other packages,
like /usr/bin/man, /usr/bin/makewhat or /usr/share/man/man7/man.7.gz.

An attempt was made to use update-alternatives to avoid conflicts.
Update-alternatives is pretty fragile though. Right now mandoc tries to install
/usr/share/man/man7/man.7.gz as slave of /usr/bin/man. However, since the man
pages comes from the man-pages packages, and the binary from the man package,
it is not actually a slave. So update-alternatives fails and mandoc is not
functional at all as update-alternatives doesn't install any of the other
symlinks at all if one fails.

How about simply conflicting instead of using the fragile update-alternative
way? I somehow doubt that having both man and mandoc has much benefit anyways?