Made near-jump check more strict in LoadNamedFieldPolymorphic on ia32/x64. (Chromium issue 134055)

Fixed lazy sweeping heuristics to prevent old-space expansion. (issue 2194)

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@11909 ce2b1a6d-e550-0410-aec6-3dcde31c8c00