Remove redundant usages of some macros and functions in debug.cc

Cleanup of HEAP and FACTORY macros and use isolate_ member of classes where it is possible.
Cleanup of debugger(), debug() and global_handles() functions.
Pass the isolate pointer to the HandleScope constructor.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6708108

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7416 ce2b1a6d-e550-0410-aec6-3dcde31c8c00