runtime/race: print more informative message on goroutine exhaustion

[dvyukov]

Currently programs with -race fail with:
==1815==ThreadSanitizer: Thread limit (8192 threads) exceeded. Dying.


There is a limit on amount of simultaneously alive goroutines.
We need to print a more informative message, add a link to a web page saying what to do
in this case.
Probably remove "ThreadSanitizer" since the race detector is not branded as
ThreadSanitizer.
Look into increasing this limit to say 16K.

[rsc]

Comment 1:

Labels changed: added go1.3maybe.

[rsc]

Comment 2:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 3:

Labels changed: added repo-main.

[dvyukov]

Race detector now prints:
race: limit on 8192 simultaneously alive goroutines is exceeded, dying