_filedir*: Add link to bash-bug discussion about complete -X case sensitivity.

bash_completion

@@ -633,6 +633,7 @@ _filedir()
 
     if [[ "$1" != -d ]]; then
         # Munge xspec to contain uppercase version too
+        # http://thread.gmane.org/gmane.comp.shells.bash.bugs/15294/focus=15306
         xspec=${1:+"!*.@($1|${1^^})"}
         toks+=( $( compgen -f -X "$xspec" -- $quoted ) )
     fi
@@ -1722,6 +1723,7 @@ _filedir_xspec()
         ))
 
     # Munge xspec to contain uppercase version too
+    # http://thread.gmane.org/gmane.comp.shells.bash.bugs/15294/focus=15306
     eval xspec="${xspec}"
     local matchop=!
     if [[ $xspec == !* ]]; then