Version Control With Subversion Source

Update some text which implies 1.6 is the most recent version.

* en/book/ch04-branching-and-merging.xml
(svn.branchmerge.cherrypicking,
(svn.branchmerge.advanced.blockchanges):
* en/book/ch05-repository-admin.xml
(svn.reposadmin.basics.backends.fsfs.revfiles,
svn.reposadmin.maint.diskspace.fsfspacking):
Like it says at the top.

* en/book/ch04-branching-and-merging.xml
(svn.branchmerge.basicmerging.mergeinfo.inheritance): Add an index
entry for 'subtree mergeinfo' referencing the sidebar on that very
topic.

Without going too crazy, try to explain subtree merges
and subtree mergeinfo.

* en/book/ch04-branching-and-merging.xml
(svn.branchemerge.basicmerging.stayinsync.subtree): New sidebar
covering the basics of subtree merges and subtree mergeinfo.

(svn.branchmerge.basicmerging.mergeinfo.inheritance): Add an id
attribute to the sidebar on mergeinfo inheritance, so we can
reference it from the new sidebar above.

Grammar tweak

"developers that edit" -> "developers who edit"

Merge the relevant portions of r4137 from ^/trunk/en.

Merge the relevant portions of r4136 from ^/trunk/en.

Document some options which lacked documentation:

* svnadmin's --config-dir, --deltas, --fs-type, and --wait

* svnlook's --diff-copy-from, --extensions, --full-paths, --limit,
--non-recursive, --verbose, and --xml

Also, flesh out the documentation for svn's --extensions option for
completeness and correctness.

Finally, finish the work of replacing statically listed subcommand
options with xref's to their descriptions.

* en/book/ch09-reference.xml
Document the --ignore-whitespace, --native-eol, --reverse-diff,
--strip, and --summarize options.

Clever or insane? You decide.

* en/book/ch09-reference.xml
Add id="" to all 'svn' option descriptions, and replace static text
in each subcommand's Option section with pointers to these IDs. As
an unexpected side-effect, the resulting ID mapping failures
identified a number of options that were not yet described in the
reference chapter.

* en/book/ch04-branching-and-merging.xml

(svn.branchmerge.basicmerging.mergeinfo): Add a sidebar on mergeinfo
inheritance.

(svn.branchmerge.nomergedata): Tweak 'Natural History and Implicit
Mergeinfo' sidebar to account for the fact that we already defined
'explicit mergeinfo'.