Version Control With Subversion Source

* src/en/book/ch03-advanced-topics.xml
(svn.advanced.externals): Fix a revision number glitch in
the example output, and simply say "external" instead of
"file external" where the context prevents ambiguity.

* src/en/book/ch03-advanced-topics.xml
(svn.advanced.externals): Add new material about file externals,
borrowing pieces from the 1.6 release notes where applicable.

* src/en/book/ch08-embedding-svn.xml
(svn.developer.usingapi.otherlangs): Put a URL into a sentence,
since we don't like having free-floating URLs in our book.

* src/en/book/ch08-embedding-svn.xml
(svn.developer.usingapi.otherlangs): SVNKit has been open source
for some time. Update the comparison between SVNKit and JavaHL
to reflect this fact.

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn merge" (cf. http://www.svnbook.de/report/6).

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn lock" (cf. http://www.svnbook.de/report/6).

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn list" (cf. http://www.svnbook.de/report/6).

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn info" (cf. http://www.svnbook.de/report/6).

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn import" (cf. http://www.svnbook.de/report/6).

* trunk/src/de/book/ch09-reference.xml
- Ticket #262 command "svn help" (cf. http://www.svnbook.de/report/6).