Updated VM stacktrace support (20898) with strndup impl.

Updated VM stacktrace support (20898) with platform-
independent version of strndup.
Committed: https://code.google.com/p/dart/source/detail?r=20936

[Tom Ball, 2013-04-03 23:11:39]

This CL is the same as 20898, except I replaced use of strndup, which isn't
available on Windows, with my own Strndup().

[Tom Ball, 2013-04-03 23:12:04]

The new Strndup is in isolate.cc.

[siva, 2013-04-04 00:04:15]

lgtm

[siva, 2013-04-04 00:42:59]

Actually a better solution might be to add your new
strndup implementation to platform/c99_support_win.h
and not have this variant called Strndup.

[Tom Ball, 2013-04-04 18:48:04]

On 2013/04/04 00:42:59, siva wrote:
> Actually a better solution might be to add your new
> strndup implementation to platform/c99_support_win.h
> and not have this variant called Strndup.

Good idea -- I moved it as you suggested, and verified that it builds and tests
pass on Windows.

[Tom Ball, 2013-04-04 18:48:31]

Committed patchset #2 manually as r20936 (presubmit successful).