test-path-util: fix another stupid test failure
Revert "build-sys: substitute strings in systemd.unit(5)"

This reverts commits c78ab91132aab9193f3c17a9a206f8825ff4be84
and 185c3be03cec26023acc11b49553753aa7330a1d.

It is simpler to just use includes...
build-sys: generate sed substitution from a list

I want to use the substitutions in different form for
xml entities.
build-sys,man: use XML entities to substite strings

This makes it easier to add substitutions to man pages,
avoiding the separate transformation step.

mkdir -p's are removed from the rule, because xsltproc will
will create directories on it's own.

All in all, two or three forks per man page are avoided,
which should make things marginally faster.

Unfortunately python parsers must too be tweaked to handle
entities. This isn't particularly easy: with lxml a custom
Resolver can be used, but the stdlib etree doesn't support
external entities *at all*. So when running without lxml,
the entities are just removed. Right now it doesn't matter,
since the entities are not indexed anyway. But I intend to
add indexing of filenames in the near future, and then the
index generated without lxml might be missing a few lines.
Oh well.
build-sys: force Python to write UTF-8

Here is a patch that fixes documentation with python 3.x in non utf-8
locales.  Specifically in my locale latin-1 is the default setting for
output going to stdout, which causes it to fail. By writing directly
to file we are able to set the locale to utf-8.