Allow all auto imports to be suppressed at once

This patch introduces the no_auto_import attribute:

    -compile(no_auto_import).

Useful for code generation tools that always use the
qualified function names and want to avoid the auto
imported functions clashing with local ones.

Implementation wise, we chose to have a special flag
'all' to avoid doing many set lookups when checking for
suppression.
Shell: expand 0-arity functions all the way to closing parenthesis

`erl` has tab completion for modules' exported functions but expands
only up to the opening paren. This commit closes that opening paren
in case the function is of arity zero and there is no other function with
the same name. It browses the lists of matches (a 2nd time) for Arity,
on complete match and then decides what to append.
stdlib/lists: Add function droplast/1
This functions drops the last element of a non-empty list.

lists:last/1 and lists:droplast/1 are the dual of hd/1 and tl/1 but
for the end of a list.
Added tests for lists:droplast/1 to stdlib/lists_SUITE
Added documentation of lists:droplast/1
Import and use lists:droplast/1 in v3_core/v3_kernel

Also imported lists:last/1, and removed the local definition.
Use lists:droplast/1 in orber/orber_interceptors.erl
lib/wx - Replace reverse(tl(reverse(L))) with lists:droplast/1
lib/ssh - Replace reverse(tl(reverse(L))) with lists:droplast/1
Issue a warning when a named fun is constructed but not used
Add a spec for a function that does not return
Shut off a dialyzer unmatched return warning

Dialyzer does not like list comprehensions for which the result is not
assigned to some variable (maybe anonymous).  In this particular case,
the comprehension, containing only a filter but no generator, was used
to save some lines, but IMO this type of code, while "cute", is not so
easy to comprehend.
compiler: Strengthen Maps tests
compiler: Strengthen listings tests
v3_core: Annotate list comprehensions to help out dialyzer
compiler: Fold binary Map key patterns to literals
compiler: Teach beam_disasm has_map_field instruction
Document maps-related abstract syntax trees

	{map,Loc,Fields}
	{map,Loc,Argument,Fields}

	{map_field_assoc,Loc,Name,Value}
	{map_field_exact,Loc,Name,Value}
Complete support of maps in erl_syntax

	map_expr/1
	map_expr/2
	map_expr_argument/1
	map_expr_fields/1

	map_field_assoc/2
	map_field_assoc_name/1
	map_field_assoc_value/1

	map_field_exact/2
	map_field_exact_name/1
	map_field_exact_value/1
Handle map fields in their own function in erl_eval

Map fields (K := V, K => V) are not expressions and shouldn't be clauses of
erl_eval:expr/5.