Version Control With Subversion Source

* en/book/ch02-basic-usage.xml
(svn.tour.history.log): Let's mention new `--search` &
`--search-and` options of `svn log` command.

There is a chance that the relevant paragraphs from svn.ref.xml
(svn.c.log) should be moved to ch02-basic-usage.xml
(svn.tour.history.log).