[Pig Wiki] Update of "HowToContribute" by XuZhang

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The following page has been changed by XuZhang:
http://wiki.apache.org/pig/HowToContribute

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      * Code should be formatted according to [http://java.sun.com/docs/codeconv/ Sun's conventions].  We use four spaces ('''not''' tabs) for indentation.
      * Contributions should pass existing unit tests.
      * New unit tests should be provided to demonstrate bugs and fixes. [http://www.junit.org/ JUnit] is our test framework:
-           * You must implement a class that extends junit.framework.TestCase and whose class name starts with Test.
+           * You must implement a class that extends `junit.framework.TestCase` and whose class name contains `Test`.
-           * Define methods within your class whose names begin with test, and call JUnit's many assert methods to verify conditions; these methods will be executed when you run ant test.
+           * Define methods within your class and annotate it with `@Test`, and call JUnit's many assert methods to verify conditions; these methods will be executed when you run `ant test`.
-           * Place your class in the test tree.
+           * Place your class in the test tree. 
-           * you can run all the unit test with the command `ant -Djunit.hadoop.conf=<dir> test` where `dir` is location of `hadoop-site.xml` of your cluster. Similarly, you can run a specific unit test with the command `ant Djunit.hadoop.conf=<dir> test -Dtestcase=<ClassName>` (For example `ant -Djunit.hadoop.conf=/home/hadoop test -Dtestcase=TestPigFile`)
+           * you can then run all the unit test with the command `ant test`. Similarly, you can run a specific unit test with the command `ant test -Dtestcase=<ClassName>` (For example `ant test -Dtestcase=TestPigFile`)
  
  == Generating a patch ==
  === Compilation ===