build-sys: warn if people don't change the default NTP servers when building systemd Also, explain the situation in the docs. Relates to #437

DISTRO_PORTING: add full path for /usr/lib/systemd/systemd and fix grammar (David: fixed up some trailing whitespace and commit-message)

man: wording and grammar updates This is a recurring submission and includes corrections to various issue spotted.

build-sys: fix spelling of sysvrcndir

build-sys: drop all distribution specfic checks Yay, we now have a completely generic systemd. No distribution specific checks anymore!

DISTRO_PORTING: correct location of hostname-setup.c f33d3ec1 (move more common files to shared/ and add them to shared.la, 2012-04-12) moved src/hostname-setup.c to src/shared/hostname-setup.c, but did not update DISTRO_PORTING accordingly. Fix this.

main: replace --running-as= by --session and --system do mimic related tools and D-Bus

typo: the correct spelling is maintenance not maintainance

docs: update DISTRO_PORTING a little

docs: add terse distribution porting guide