Truly test debugger in erl_eval_SUITE copy

The module was not interpreted.

This surfaced two bugs, related to shadowed variables in binary patterns in
comprehension generators, and guard filters not properly detected. The guard
detection code from dbg_iload is deleted in favor of erl_lint:is_guard_test/1.
The erl_lint module is now safe to use because it can handle all expressions
emitted by sys_pre_expand, the following warning is thus obsolete and has been
removed from code:

	%% Cannot use erl_lint here as sys_pre_expand has transformed source.