Update RealSystemFacade.java

fix bug: getMaxBytesOverMobile() will return a negative value at runtime.
change DOWNLOAD_MAX_BYTES_OVER_MOBILE, add 'L' at the end. 
(Android Studio 0.5.8 with Android SDK Build-tools 19.1 on Mac OSX 10.9.3)
Merge pull request #5 from pcqpcq/patch-1

Update RealSystemFacade.java