DERBY-5200: embellish build.xml to automatically install junit.jar in the correct directory if it doesn't exist
DERBY-5200: embellish build.xml to automatically install junit.jar in
the correct directory if it doesn't exist

Update the build instructions with information about the automatic
downloading of junit.jar.


git-svn-id: 2c06e9c5008124d912b69f0b82df29d4867c0ce2@1102645 13f79535-47bb-0310-9956-ffa450edef68

trejkaz/derby,apache/derby,apache/derby,apache/derby,apache/derby,trejkaz/derby,trejkaz/derby