HttpServer: improve handling of finished HTTP exchanges

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TEST: sun/net/www/protocol/http/B5017051.java
JDK under test: (/tmp/jprt/P1/T/222116.ss145989/testproduct/solaris_sparcv9_5.10-product)
java version "1.7.0-internal"
Java(TM) SE Runtime Environment (build 1.7.0-internal-201103082221.ss145989.tl-pit-2d-awt-swin-b00)
Java HotSpot(TM) 64-Bit Server VM (build 21.0-b03, mixed mode)

ACTION: build -- Passed. Build successful
REASON: Named class compiled on demand
TIME: 0.253 seconds
messages:
command: build B5017051
reason: Named class compiled on demand
elapsed time (seconds): 0.253

ACTION: compile -- Passed. Compilation successful
REASON: .class file out of date or does not exist
TIME: 0.252 seconds
messages:
command: compile /tmp/jprt/P1/T/222116.ss145989/source/jdk/test/sun/net/www/protocol/http/B5017051.java
reason: .class file out of date or does not exist
elapsed time (seconds): 0.252

ACTION: main -- Failed. Execution failed: `main' threw exception: java.lang.AssertionError
REASON: User specified action: run main/othervm B5017051
TIME: 1.2 seconds
messages:
command: main B5017051
reason: User specified action: run main/othervm B5017051
elapsed time (seconds): 1.2
STDOUT:
Response code from Part 1 = 200 OK
STDERR:
java.lang.AssertionError
at sun.net.httpserver.ServerImpl.closeConnection(ServerImpl.java:467)
at sun.net.httpserver.ServerImpl.access$1100(ServerImpl.java:45)
at sun.net.httpserver.ServerImpl$Exchange.run(ServerImpl.java:642)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
STATUS:Failed.`main' threw exception: java.lang.AssertionError

TEST RESULT: Failed. Execution failed: `main' threw exception: java.lang.AssertionError
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