- 32-bit Linux already seems to scatter the mmap() chunks around; 64-bit didn't.
- Seed the system random number generator a little better (we needlessly
trunctaed microsecond resolution to millisecond resolution).
- Will automatically take advantage of better entropy when V8::RandomPrivate
uses it.

BUG=v8:805

Review URL: http://codereview.chromium.org/7377008
Patch from Chris Evans <cevans@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8702 ce2b1a6d-e550-0410-aec6-3dcde31c8c00