Version Control With Subversion Source

feature which has been reverted from Subversion.

* en/book/ch07.xml (svn-ch-7-sect-2.3.4): Rewrite wording to preserve good bits of
r1203 whilst removing parts that spoke specifically about canonicalization.
Undo some over-enthusiastic standardization from r1203 - say "abbreviated" not
"also specified" in the HeadURL/URL case.