miner.stop threadCount actually required

[aakilfernandes]

https://github.com/ethereum/go-ethereum/wiki/JavaScript-Console#minerstop

Documentation says its optional, however when I try in 1.4.0-unstable its actually required

[karalabe]

This should be fixed now. @aakilfernandes Please verify latest develop if it indeed works correctly for you.