test/net/imap/test_imap.rb (test_exception_during_idle): kill infinite looper

It is possible for Mutex#sleep (via ConditionVariable#wait)
to prematurely wake up under MJIT (because Mutex#sleep can't
handle spurious wakeups).  This affects @idle_done_cond in
Net::IMAP#idle and means the response handler may never
set `in_idle' to `true`.

In any case, ensure the infinite looping `raiser' thread
stops running when the test is done.

Will work on reducing the effect of spurious wakeups from
MJIT...

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64387 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/net/imap/test_imap.rb

@@ -231,7 +231,7 @@ class IMAPTest < Test::Unit::TestCase
         in_idle = false
         exception_raised = false
         c = m.new_cond
-        @threads << Thread.start do
+        raiser = Thread.start do
           m.synchronize do
             until in_idle
               c.wait(0.1)
@@ -243,6 +243,7 @@ class IMAPTest < Test::Unit::TestCase
             c.signal
           end
         end
+        @threads << raiser
         imap.idle do |res|
           m.synchronize do
             in_idle = true
@@ -260,6 +261,7 @@ class IMAPTest < Test::Unit::TestCase
       imap.logout
     ensure
       imap.disconnect if imap
+      raiser.kill unless in_idle
     end
   end