Version Control With Subversion Source

Tweak an xref to point to a more relevant related section.

Tweaks made or suggested by Eric Hanchrow.

Make 'backdate' into a <firstterm>, with a concise explanation.

Tweaks from Eric Hanchrow, plus some new stuff on language bindings.

Commit a bunch of tweaks from Eric Hanchrow's review of chapter 3.

Add a note about scheme vs. schema to HACKING.

* book/ch07-customizing-svn.xml
Document the http-proxy-exceptions runtime configuration option.
Oversighted noted by Neil Mayhew <neil_mayhew@...>.

Add skeletal svnsync reference matter.

Fork the homepage into a page devoted to older versions.

Minor fixes suggested by cmpilato.