Version Control With Subversion Source

* src/en/book/ch09-reference.xml
By way of followup to r3264, use a capitalization and sentence
structure pattern consistent with other bits of the mod_X_svn
directive descriptions. Also, bind the xref that talks about
disabling authz checks more tightly with the "Off" directive value.

Finish Trac ticket #125 (Document SVNPathAuthz short_circuit), and add
a section for mod_authz_svn directives to the reference chapter.

* en/book/ch09-reference.xml
(svn.ref.mod_dav_svn): Fix the SVNPathAuthz directive to not claim
to have a file-path value -- it's values are "On", "Off", or (the
newly-added) "short_circuit".
(svn.ref.mod_authz_svn): New section for mod_authz_svn directives.

More stylesheet tweaks.

Kill all named fonts in our HTML stylesheets. Let the user's
preferences win. While here, switch to serif'ed fonts for the body.

* src/en/book/ch06-server-configuration.xml
Re-add periods to a set of list items for consistency with the five
other similar, neighboring lists. Also, don't say "CGI software"
because not all repository browsing software technically uses the CGI
interface.

Add another special character.

* src/en/book/ch04-branching-and-merging.xml
Rework helpful table to a) not have trailing periods in the left
column, and b) use proper tagging in the right one.

Convert icon descriptions back to full sentences.

Tweak-a-word here, tweak-a-word there, tweak-a-word everywhere.

More work to try to make our HTML stylations match the way O'Reilly
renders text.

* src/en/book/styles.css
Override <strong> tags -- we have no markup that should be
generating bold text. Italicize commands. Shrink the fonts in
admonishments.