builder.isSingleFile should be a bool, not an int.

git-svn-id: file:///data/workdir/Transmission-svn//trunk@14287 1bcf1a7e-6170-4b50-b784-84ec52b2dec6
separate out the sandbox code so that test sandboxes can be created without a tr_session

git-svn-id: file:///data/workdir/Transmission-svn//trunk@14288 1bcf1a7e-6170-4b50-b784-84ec52b2dec6