When the number of parameters times 4 (kPointerSize) to a function cannot be encoded in 12 bits the return sequence gets one more instruction. Changed the assertion to check for this case.

BUG=http://code.google.com/p/v8/issues/detail?id=492
TEST=test/mjsunit/regress/regress-492.js
Review URL: http://codereview.chromium.org/354028

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3211 ce2b1a6d-e550-0410-aec6-3dcde31c8c00