comment added; summary, type, milestone changed

• summary changed from Profiling a threaded application with GHC-6.6rc. to Profiling doesn't work with -threaded
• type changed from bug to task
• milestone changed from 6.6 to 6.6.1

The profiling subsystem isn't thread-safe at all, so can't be used with -threaded. I've made GHC 6.6 emit an error and refuse to compile rather than generate a crashing binary.

Later, we should fix this. A Big Giant Lock around the profiling subsystem is probably sufficient - it will introduce a bottleneck with -N2 and greater, but it should be ok with single processor runs.