This doesn't actually compile, since it's missing a `+` at the end of the line, so merging this commit broke the build:

```
[error] /Users/joshrosen/Documents/spark/spark/core/src/main/scala/spark/storage/BlockManagerMasterActor.scala:125: type mismatch;
[error]  found   : Long
[error]  required: Int
[error]           (now - info.lastSeenMs) + "ms exceeds " + slaveTimeout + "ms")
[error]                ^
[error] one error found
```