[control.pir] take without gather now warns

Before this commit, a 'take' without a (dynamically) enclosing 'gather'
block halted the program without explanation. This commit makes the
condition non-fatal and adds a warning message. Tene++ for guidance.

perl6.pir

@@ -214,7 +214,7 @@ and report exceptions.
     .get_results (exception)
     $I0 = exception['severity']
     if $I0 == .EXCEPT_EXIT goto exit
-    if $I0 != .EXCEPT_WARNING goto not_warning
+    if $I0 > .EXCEPT_WARNING goto not_warning
     printerr exception
     printerr "\n"
     $P0 = exception["resume"]

src/builtins/control.pir

@@ -85,6 +85,7 @@ the moment -- we'll do more complex handling a bit later.)
     $P0         = root_new ['parrot';'Exception']
     $P0['type'] = .CONTROL_TAKE
     $P0['severity'] = .EXCEPT_NORMAL
+    $P0['message'] = 'take without gather'
     setattribute $P0, 'payload', value
     throw $P0
     .return (value)