Version Control With Subversion Source

Synchronise the English and Norwegian svnbook with "make sync". Updated
changes between r1223:1240.

* src/nb/LAST_UPDATED
Updated to 1240 by "make sync".

* src/nb/README
Merged r1228.

* src/nb/REVIEW
Merged r1229.

* src/nb/TODO
Merged r1231, r1232, r1233, r1234.

* src/nb/book/ch04.xml
Merged and updated r1231, r1232, r1235, r1238. New "The Key Concept
Behind Merging" section.

* src/nb/book/ch06.xml
Merged r1232.

Update the revision number in src/nb/LAST_UPDATED to 1223 to get past
the replacement of Makefile when running "make sync".

* src/nb/LAST_UPDATED
Updated to "1223".

Sync between English and Norwegian version: Merge changes between
r1214:1221 from src/en to src/nb . Can’t use the usual "make sync",
nb/Makefile gets into a strange non-revertable state because of the
replace in r1223, so it has to be tweaked manually.

* src/nb/LAST_UPDATED
Manually set to 1221.

* src/nb/book/ch07.xml
* src/nb/book/ch08.xml
Merged r1219.

Small fix to a bug noticed by Robert Tasarz (robert.tasarz@...).

Book Spanish. Translated 12 paragraphs.

German Book: Change revision number from what it used to be when the book was
part of the Subversion repository, to the actual revision number that it became
when the book moved into its own repository.

* de/book/book.xml: r7314 there is r353 here.

Followup to r1231, which changed some section ids. Repoint an xref which was
now pointing to the wrong place.

* en/book/ch04.xml: Fix <xref>.

* src/en/TODO: start scoping 1.2 doc work.

* src/en/TODO: divvy up the remaining 1.1 doc work among ben/fitz/mike.

* src/en/book/ch04.xml:

- don't use HEAD in merge command examples, it's not really a
good practice to encourage.

* src/en/book/ch06.xml:

- mention pre-commit hooks as an option for controlling per-dir
write access with svnserve.

- Merge the too-short "external path-based authz" section into
this paragraph.

- (Servers and Permissions: A Word of Warning): remove
assumption that all repositories are BDB-based.

* src/en/TODO: remove some TODOs.
also, move a TODO from me to fitz, since it's chapter 3.