Never clear debug-stub call ICs. Make a clear distinction between is_debug_stub
used everywhere but the debugger, and IsDebugBreak, used by the debugger.

R=yangguo@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23361014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16269 ce2b1a6d-e550-0410-aec6-3dcde31c8c00