[http://googlewebmastercentral.blogspot.com/2010/04/to-slash-or-not-to-slash.html](Google: To Slash or Not to Slash)
https://gist.github.com/ericrasch/5628437#comment-1002954
# 2013-08-29 Eric R.: trailing slash fix SRC: http://stackoverflow.com/a/1668741/284091
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*(?:[^/]|\.php|\.html?))$ $1/ [L,R=301]