Unified CallWrapper and PostCallGenerator classes, the former is a

Unified CallWrapper and PostCallGenerator classes, the former is a
generalization of the latter. This makes CallWrapper architecture-independant,
so it can be pulled up into assembler.h, nuking 3 copy-n-paste classes. Only a
small improvement, but nevertheless...
Review URL: http://codereview.chromium.org/6893156

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7758 ce2b1a6d-e550-0410-aec6-3dcde31c8c00