Fix step commands that mix running threads and stepping threads.
Fix step commands that mix running threads and stepping threads.

This fixes https://github.com/tfiala/lldb/issues/62.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@227915 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb