Fix code gen bug on arm and mips; SeqStringSetChar overwrites a register; Add better default PrintDataTo for HInstruction
BUG=

Review URL: https://codereview.chromium.org/14895019

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14710 ce2b1a6d-e550-0410-aec6-3dcde31c8c00