Rudimentary jar watching

New options watchJars takes a colon separated list of jars
(just the jar names, not paths).  For example:

-Dspringloaded=watchJars=foo.jar:bar.jar

Committed some very basic tests that are passing, they are in
the SpringLoadedTestsInSeparateJVM test class, see the
tests with 'jar' in the name.

testdata/jars/README

@@ -0,0 +1 @@
+For the watching/updating from jars feature, these are the jar testdata

testdata/jars/one/Bar.java

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+package test;
+public class Bar {
+  public static void run() {
+    new Wibble().foo();
+  }
+}

testdata/jars/one/Foo.java

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+public class Foo {
+  public static void run() {
+    m();
+  }
+  public static void m() {
+    System.out.println("m() running");
+  }
+}

testdata/jars/one/Wibble.java

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+package test;
+public class Wibble {
+  public void foo() {
+    System.out.println("Wibble.foo() running, version 1");
+  }
+}

testdata/jars/one/build.sh

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+javac -d . *.java
+jar -cvMf foo.jar Foo.class
+jar -cvMf bar.jar test/*.class
+

testdata/jars/two/Bar.java

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+package test;
+public class Bar {
+  public static void run() {
+    new Wibble().foo();
+  }
+}

testdata/jars/two/Foo.java

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+public class Foo {
+  public static void run() {
+    n();
+  }
+  public static void n() {
+    System.out.println("n() running");
+  }
+}

testdata/jars/two/Wibble.java

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+package test;
+public class Wibble {
+  public void foo() {
+    System.out.println("Wibble.foo() running, version 2");
+  }
+}

testdata/jars/two/build.sh

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+javac -d . *.java
+jar -cvMf foo.jar Foo.class
+jar -cvMf bar.jar test/*.class
+