Version Control With Subversion Source

README.txt instead of README, and they use local eol style in those
files. This revision makes the analogous change to
~/.subversion/README, and adjusts the book for all of these changes
(thanks to Mike Pilato for reminding me of the docs):

* subversion/libsvn_subr/config_impl.h
(SVN_CONFIG__USR_README_FILE): Add .txt extension.

* subversion/libsvn_subr/config_file.c
(svn_config_ensure): Use APR_EOL_STR instead of "\n".

* doc/book/book/ch05.xml, doc/book/book/ch06.xml,
doc/book/book/ch08.xml: Use the new filenames.