Version Control With Subversion Source

* src/en/book/ch02-basic-usage.xml,
* src/en/book/ch03-advanced-topics.xml,
* src/en/book/ch04-branching-and-merging.xml,
* src/en/book/ch09-reference.xml
Fix some examples which used subcommand short-forms ("co") instead
of the full subcommand ("checkout").

Patch by: quinntaylor@...

* src/en/book/ch09-reference.xml
Xref-ify a mention of 'svn switch', and cleanup an example a bit.

Patch by: quinntaylor@...

Finish issue #41 ("Inconsistent links from subcommand help to
reference chapter").

* src/en/book/ch02-basic-usage.xml
Also suggest running 'svn help <subcommand>' in a couple of places
where we also have a pointer to the reference chapter.

Patch by: quinntaylor@...

* src/en/book/ch06-server-configuration.xml
Some more cleanup related to issue #87.

Patch by: quinntaylor@...

* src/en/book/ch09-reference.xml
Document the --trust-server-cert global option.

* src/en/book/ch06-server-configuration.xml
Continuing a trend of consistification started by Quinn Taylor's
recent patches to this chapter, explicitly label and comment on the
authentication and authorization blocks of the httpd.conf examples.

Finally finish issue #87 ("ch06: mention 'htdigest' tool when
mentioning digest auth").

* src/en/book/ch06-server-configuration.xml
Break coverage of the Digest authentication type out into its own
section, and clean up / consistify other related text.

Patch by: quinntaylor@...
(Tweaked by me.)

* src/en/book/ch02-basic-usage.xml
Avoid redundant descriptions of common 'svn status' codes.

Markup corrections only.

* src/en/book/appb-svn-for-cvs-users.xml
Lose redundant (and ill-marked-up) information.