util.h is now about logarithms only, so we can rename it. Many files included
util.h for no apparent reason… Those includes are dropped.

The symlinks under /run/udev/static_node-tags are pointing to the
corresponding device nodes. Let's read the symlinks.

As in the previous commit, 'de' is used as the iterator variable name.

Strictly speaking, we are returning the size of a memory chunk of
arbitrary size, so ssize_t is more appropriate than int.

The files are used by logind and udevd. And the functions in the files
are not specific to logind, and quite general enough to move to
libshared.