Check if a AVAILABLE state entry is in cache before throwing out the IllegalStateException.

org.apache.openejb.core.managed.SimpleCache.checkIn(K) {
...

switch (entry.getState()) {
case AVAILABLE:
throw new IllegalStateException("The entry " + key + " is not checked-out");
..

}

In some mutiple thread cases, I noticed that a checked entry was checked in again by other thread. then we will get a invalid illegalStateException.