Add "src" folder to source folders of org.eclipse.jgit.test

Otherwise MergeCommandTest using Sets doesn't compile in Eclipse since
adbcbc79 moved Sets from the "tst" to the "src" folder.

Change-Id: I661b987513365a8af0b568ec95b0898e5758f59f
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/.classpath

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <classpath>
 	<classpathentry excluding="**/*.idx|**/*.pack" kind="src" path="tst"/>
+	<classpathentry kind="src" path="src"/>
 	<classpathentry kind="src" path="tst-rsrc"/>
 	<classpathentry kind="src" path="exttst"/>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.7"/>