Enabled full System Loader support in executeConfigFile
Enabled full System Loader support in executeConfigFile

Enabled full System Loader support in executeConfigFile in builder.js. This allows multiple System.config invocations to have full access to the System Loader API. The use case for this commit is to be able to load additional config files which add additional used defined mapped paths that incorporate existing normalized paths from loaded package dependencies.
alexisvincent/builder,alexisvincent/builder,jrauschenbusch/builder,whitneyit/builder,jrauschenbusch/builder,lookfirst/builder,lookfirst/builder,alexisvincent/builder,systemjs/builder,jrauschenbusch/builder,systemjs/builder,systemjs/builder,douglasduteil/builder,douglasduteil/builder,whitneyit/builder