ri: Rename ri_get_methods helper to add leading underscore

Completions generally name the identifiers they export with a leading
'_' to avoid clashing with user functions.  The only exception is this
helper function in the "ri" completion script; fix it.

Reported-by: Felipe Contreras <felipe.contreras@gmail.com>

completions/ri

@@ -1,7 +1,7 @@
 # ri completion for Ruby documentation                     -*- shell-script -*-
 # by Ian Macdonald <ian@caliban.org>
 
-ri_get_methods()
+_ri_get_methods()
 {
     local regex
 
@@ -56,7 +56,7 @@ _ri()
         method=${cur#*$separator}
         classes=( $class )
         prefix="-P $class$separator"
-        ri_get_methods
+        _ri_get_methods
         return 0
     fi
 
@@ -82,7 +82,7 @@ _ri()
 
     # we're completing on methods
     method=$cur
-    ri_get_methods
+    _ri_get_methods
 } &&
 complete -F _ri ri