Changed fuzzer to randomly remove half of the arguments when running

Changed fuzzer to randomly remove half of the arguments when running
on functions that takes five or more arguments. Original version runs
for a long time when there is 5 arguments in a runtime function (45+
seconds). The fuzzer can be run with all arguments on all functions
regardless of the number of arguments by setting
RUN_WITH_ALL_ARGUMENT_ENTRIES to true in fuzz-natives.js

Review URL: http://codereview.chromium.org/598011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3819 ce2b1a6d-e550-0410-aec6-3dcde31c8c00