com.sun.net.httpserver does not catch
RejectedExecutionException and it does not close connections. We must
catch this exception to close a socket.


* steps to reproduce with attached files
 1. java -Djava.util.logging.config.file=logging.properties SmallHttpServer
 2. post tcp connections by curl or other ways
     e.g.: while true; do curl -XPOST --noproxy 127.0.0.1
http://127.0.0.1:8080/; done
 3. wait RejectedExecutionException occurs as below and then
SmallHttpServer stops by this issue.
----
Nov 05, 2016 12:01:48 PM sun.net.httpserver.ServerImpl$Dispatcher run
FINER: Dispatcher (7)
java.util.concurrent.RejectedExecutionException: Task
sun.net.httpserver.ServerImpl$Exchange@37b50d9e rejected from
java.util.concurrent.ThreadPoolExecutor@1b3178d4[Running, pool size =
1, active threads = 0, queued tasks = 0, completed tasks = 7168]
        at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(java.base/ThreadPoolExecutor.java:2076)
        at java.util.concurrent.ThreadPoolExecutor.reject(java.base/ThreadPoolExecutor.java:842)
        at java.util.concurrent.ThreadPoolExecutor.execute(java.base/ThreadPoolExecutor.java:1388)
        at sun.net.httpserver.ServerImpl$Dispatcher.handle(jdk.httpserver/ServerImpl.java:440)
        at sun.net.httpserver.ServerImpl$Dispatcher.run(jdk.httpserver/ServerImpl.java:405)
        at java.lang.Thread.run(java.base/Thread.java:844)
(SmallHttpServer is stopping by not closing socket)