when a properties file is not otherwise explicitly specified,
the sbt.version from project/build.properties is used to select
the default properties file to use. This launcher should be able
to launch:
0.7.x
0.10.{0,1}
0.11.{0,1,2,3}
0.12.x
Note that it can only launch the release versions of 0.10 and 0.11
listed above and in particular cannot launch snapshot versions. All
0.12.x versions and 0.7.x versions should be supported, although only
0.7.7 was tested.