[SPARK-1089] fix the problem in 0.9 that  ADD_JARS value was not recognized

https://spark-project.atlassian.net/browse/SPARK-1089

load jar in process() and work around for scala issue

The reason of this bug is two-folds

1. in the current implementation of SparkILoop.scala, the settings.classpath is not set properly when the process() method is invoked

2. the weird behaviour of Scala 2.10, (I personally thought it is a bug)

if we simply set value of a PathSettings object (like settings.classpath), the isDefault is not set to true (this is a flag showing if the variable is modified), so it makes the PathResolver loads the default CLASSPATH environment variable value to calculated the path (see https://github.com/scala/scala/blob/2.10.x/src/compiler/scala/tools/util/PathResolver.scala#L215)

what we have to do is to manually make this flag set, (https://github.com/CodingCat/incubator-spark/blob/e3991d97ddc33e77645e4559b13bf78b9e68239a/repl/src/main/scala/org/apache/spark/repl/SparkILoop.scala#L884)