Revert "Do away with variable length memcpy to Set/Get registers in simulator"

Revert "Do away with variable length memcpy to Set/Get registers in simulator"

This reverts r21148, it broke tests in debug mode, e.g.
mjsunit/regress/regress-observe-map-cache or mjsunit/debug-stepout-scope-part5.

TBR=bmeurer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21449

[Sven Panne, 2014-05-23 07:14:11]

Committed patchset #1 manually as r21449 (tree was closed).

[Benedikt Meurer, 2014-05-23 07:14:28]

LGTM