Clean up & fix PipedInputStreamTest.

Add additional documentation where necessary.

bug: 11666814
Change-Id: I622d180c89f835e9466c7efe8f6a079c2516b73f

Conflicts:
	harmony-tests/src/test/java/org/apache/harmony/tests/java/io/PipedInputStreamTest.java
Make PipedWriter#flush throw if the reader is closed.

bug: 11666814
Change-Id: I25dc56f5e50e0cfb14e5781e953115864be612a9

Conflicts:
	harmony-tests/src/test/java/org/apache/harmony/tests/java/io/PipedWriterTest.java
Minor cleanup of deepHashCode / deepEquals.

These methods used equals() comparisons where identity
checks would've sufficient. As expected, this results in a
small but measurable performance increase on both art
& dalvik.

---------------------- After --------------
ART:
    arrayLength    benchmark      us linear runtime
              1 DeepHashCode    8.08 =
              1       Equals   17.68 =
              4 DeepHashCode    8.63 =
              4       Equals   18.20 =
             16 DeepHashCode   19.59 =
             16       Equals   41.19 =
            256 DeepHashCode  255.41 =
            256       Equals  483.61 ==
           2048 DeepHashCode 2321.91 ==============
           2048       Equals 4932.40 ==============================
Dalvik:
    arrayLength    benchmark      us linear runtime
              1 DeepHashCode    32.7 =
              1       Equals    65.3 =
              4 DeepHashCode    34.4 =
              4       Equals    67.7 =
             16 DeepHashCode    76.0 =
             16       Equals   142.8 =
            256 DeepHashCode   755.6 =
            256       Equals  1515.6 ===
           2048 DeepHashCode  6915.4 ===============
           2048       Equals 13786.6 ==============================

------------------------ Before --------------------
Art:
    arrayLength    benchmark      us linear runtime
              1 DeepHashCode    8.13 =
              1       Equals   17.86 =
              4 DeepHashCode    8.63 =
              4       Equals   18.92 =
             16 DeepHashCode   19.59 =
             16       Equals   40.89 =
            256 DeepHashCode  253.88 =
            256       Equals  477.02 ==
           2048 DeepHashCode 2795.26 ================
           2048       Equals 4962.11 ==============================

Dalvik:
    arrayLength    benchmark      us linear runtime
              1 DeepHashCode    32.8 =
              1       Equals    66.7 =
              4 DeepHashCode    34.4 =
              4       Equals    70.1 =
             16 DeepHashCode    74.1 =
             16       Equals   147.9 =
            256 DeepHashCode   805.0 =
            256       Equals  1573.2 ===
           2048 DeepHashCode  7253.4 ===============
           2048       Equals 14349.8 ==============================

bug: 9320068

Change-Id: Id73bf38dd0777b2ec9004a2941523d082bbc74c9