Version Control With Subversion Source

Add a missing closing tag.

* en/book/ch09-reference.xml
Reference docs for 'svn merge --allow-mixed-revisions'.

* en/book/ch09-reference.xml
Doc 'svn export --ignore-keywords'.

* en/book/ch09-reference.xml
Document 'svnversion --quiet' (which is apparently only useful when
combined with --version). Ho hum.

* en/book/ch09-reference.xml
Document svnsync's --config-option, --disable-locking,
--source-prop-encoding, and --steal-locks options.

* en/book/ch09-reference.xml
Clarify in the warnings about not using explicit source URLs with
'svnsync sync' and 'svnsync copy-revprops' that the danger is with
untrusted users who can change the special r0 props, not just any
ol' committer.

Suggested by: danielsh

* en/book/ch06-server-configuration.xml
Switch to source-url-having syntax for svnsync operations.

This issue touches bits of the following issues:

issue #59 ("'svnsync init' supports a --allow-non-empty flag in
Subversion 1.7")

Issue #79 ("Update 'svnsync sync' and 'svnsync copy-revprops'
syntax and recommendations.")

Issue #132 ("1.7 changes: New program, subcommands, and options")

* en/book/ch05-repository-admin.xml
Break up the "Repository Replication" section into a bit about
svnsync, a (currently empty) bit about svnrdump, and then a common
wrap-up section. In the svnsync section, discuss the
--allow-non-empty and --steal-lock options, and rework some
out-of-date material.

For issue #79 ("Update 'svnsync sync' and 'svnsync copy-revprops'
syntax and recommendations."):

* en/book/ch09-reference.xml
(svn.ref.svnsync.sw): Note the new --revision (-r) option.
(svn.ref.svnsync.c.copy-revprops, svn.ref.svnsync.c.synchronize):
Document the new syntaxes for these subcommands, adding a
recommendation (by way of warning) to each about specifying the
source URL on the command-line.

Fix unbalanced square brackets. (Karl Fogel weeps in a corner somewhere.)