Emit VMLS for multiply-subtract on ARM.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/12319113
Patch from Hans Wennborg <hans@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13748 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Set default number of sweeper threads to two.

BUG=

Review URL: https://codereview.chromium.org/12301020

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13749 ce2b1a6d-e550-0410-aec6-3dcde31c8c00