Changes to ubuntu-docs build

[Jeremy Bicha]

In Oneric trunk, I converted the ubuntu-docs build system to better
match what gnome-user-docs is doing upstream. We now build with
yelp-tools instead of gnome-doc-utils. Notably, this changes the
install location for documentation from /usr/share/gnome/help/ to
/usr/share/help/. The URI ghelp:ubuntu-help won't work; you'll need to
use help:ubuntu-help. The new build system seemed to build a bit
faster.

Also, I used itstool instead of intltool. I believe itstool works
pretty much the same as intltool but it has built-in support for
formats like Mallard and Docbook. One particular benefit of this
built-in support is that <comment> fields don't get sent for
translation. In Natty, we hacked this by converting the comments to
traditional code comments. These comments still showed up for
translators automatically as "hints" but were not themselves
translatable.

This is the command I used:
itstool C/*.page -o ubuntu-help.pot

Jeremy