Slightly adapted testBuildProjectPath:
External storage directory doesn't necessarily have to be "/mnt/sdcard/"
UtilFileTest.testFileSize: Fixed false failure with German locale
UtilFile.getSizeAsString returns a locale-aware String (as it should),
but the test compared it to a hardcoded dot, which can fail (for
instance when testing with a German locale which uses a comma).
Also made assert messages slightly more descriptive.
testBuildProjectPath: Use Constants.DEFAULT_ROOT instead of hardcoded
path.