Replace http:// links with https:// and update links when the old target no longer...

Replace  links with https:// and update links when the old target no longer exists.

* en/book/appa-quickstart.xml
  (svn.intro.install): s/http/https/ for apache.org

* en/book/appc-webdav.xml
  (svn.webdav.clients.standalone.free): www.ics.uci.edu/~webdav redirect to www.davexplorer.org
  (svn.webdav.clients.file-explorer-extensions.linux-de): s/http/https/ for gnome.org and kde.org (and kde.org seems to redirect www.k.o to k.o)
  (svn.webdav.clients.fs-impl.windows): s/http/https/ for southrivertech.com (and it seems to redirect www.s.c to s.c)
  (svn.webdav.clients.fs-impl.linux): s/http/https/ for nongnu.org

* en/book/ch00-preface.xml
  (svn.intro.righttool): s/http/https/ for git-scm.com and mercurial-scm.org (and mercurial-scm.org seems to redirect mercurial-scm.org to www.mercurial-scm.org)
  (svn.intro.history): s/http/https/ for collab.net and apache.org
  (svn.intro.whatsnew): s/http/https/ for apache.org
  (svn.preface.free): s/http/https/ for svnbook.red-bean.com

* en/book/ch03-advanced-topics.xml
  (svn.advanced.changelists): s/http/https/ for mail.google.com, www.youtube.com and www.flickr.com

* en/book/ch04-branching-and-merging.xml
  (svn.branchmerge.basicmerging.reintegrate): s/http/https/ for svnbook.red-bean.com

* en/book/ch06-server-configuration.xml
  (svn.serverconfig.httpd): s/http/https/ for apache.org
  (svn.serverconfig.httpd.authn.basic): s/http/https/ for apache.org
  (svn.serverconfig.httpd.authn.digest): s/http/https/ for apache.org
  (svn.serverconfig.httpd.authz.blanket): s/http/https/ for apache.org
  (svn.serverconfig.httpd.ssl.server): s/http/https/ for apache.org and openssl.org (and openssl.org seems to redirect openssl.org to www.openssl.org)
  (svn.serverconfig.httpd.extra.browsing.syntax): s/http/https/ viewvc.org, trac.edgewall.org and websvnphp.github.io

* en/book/ch08-embedding-svn.xml
  (svn.developer.usingapi): s/http/https/ for apache.org
  (svn.developer.usingapi.otherlangs): s/http/https/ for swig.org and svnkit.com

git-svn-id: https://svn.code.sf.net/p/svnbook/source/trunk@6057 b70f5e92-ccc6-4167-9ab2-d027528d294b