MIPS: Fix issue 2346 (order of operations in keyed store on arrays) and turn...

MIPS: Fix issue 2346 (order of operations in keyed store on arrays) and turn get-own-property-descriptor.js test into a regression test.

Port r12604 (ae837167)

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10987086
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12741 ce2b1a6d-e550-0410-aec6-3dcde31c8c00