man: typo fix
networkd: refuse to use .network files with missing Address/Gateway key

These keys are mandatory in [Address]/[Route] sections. Otherwise, we
hit an assert:

ens3: setting addresses
Assertion 'address->family == 2 || address->family == 10' failed at /build/amd64-generic/tmp/portage/sys-apps/systemd-9999-r1/work/systemd-9999/src/network/networkd-address.c:137, function address_configure(). Aborting.

Reported-by: Alex Polvi <alex.polvi@coreos.com>

At the same time make sure Route's Destination and Gateway uses the same address family.
man: document some more bus functions
swap: remove if/else with the same data path

This was introduced in e1770af812 (2012-02-03, swap: replace failure
boolean by result enum).

This just removes unneeded lines of code, no functional change.
Update .mailmap file

This commit updates email addresses of people, who are already in the
.mailmap file, so I'd assume they have sorted out their viewpoint on
privacy within the .mailmap file.

The entries for this commit have been produced using:
        # Finding out duplicates by comparing email addresses:
        git shortlog -sne |awk '{ print $NF }' |sort |uniq -d

        # Finding out duplicates by comparing names:
        git shortlog -sne |awk '{ NF--; $1=""; print }' |sort |uniq -d
shared: procfs_file_alloca: handle pid==0

when pid is set to 0 use /proc/self
util.c: use read_one_line_file where possible
bus: open user, not system, bus in bus_open_user_systemd()
bus: driverd: don't attempt to remove from empty list
hwdb: update