global-functions: $EitherOr: pass boolean value

Note that literal "true" or "false" (even without quotes) is converted
to string. So you may have to enclose it in parentheses for a boolean
value:

    > :put [ :typeof [ $EitherOr true false ] ];
    str
    > :put [ :typeof [ $EitherOr (true) (false) ] ];
    bool

global-functions.rsc

@@ -382,6 +382,9 @@
 :set EitherOr do={
   :global IfThenElse;
 
+  :if ([ :typeof $1 ] = "bool") do={
+    :return $1;
+  }
   :if ([ :typeof $1 ] = "num") do={
     :return [ $IfThenElse ($1 != 0) $1 $2 ];
   }