Fix Win32 bots - they crash/timeout on too long thread name.

Fix Win32 bots - they crash/timeout on too long thread name.
Committed: http://code.google.com/p/v8/source/detail?r=7296

[Dmitry Titov, 2011-03-21 23:06:01]

strncpy_s() actually crashes (asserts in dbg) if it is told to copy more
characters then the destination buffer allows.

The thread name is limited at 15chars + \0. So in some cases we were exceeding
that ("TerminationThread"). Need to use _TRUNCATE option with strncpy_s().

TBR=vitalyr

[Vitaly Repeshko, 2011-03-22 13:44:45]

LGTM