MIPS: Fix return-value from Array.push stub when pushing non-SMI value

Load and update the arrays length in v0 to make sure the length gets
returned correctly when leaving the function.

Add new testcase.

TEST=mjsunit/array-push-non-smi-value

BUG=130022
R=jkummerow@chromium.org, plind44@gmail.com

Review URL: https://codereview.chromium.org/23589002

Patch from fs <fs@opera.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16377 ce2b1a6d-e550-0410-aec6-3dcde31c8c00