This fixes a regression introduced in commit 805f9c89fc01220bc1bb0f27e1b68fd4eca688ba
The problem occured with map keys compiled with dialyzer option turned on.

In OTP 17, map keys needs to be literals.

A module containing two named funs bearing the same name and arity could be
miscompiled.

Reported-by: Sam Chapin

The scope is supposed to contain all variables that are currently
live. We need this information for certain optimizations to
avoid capturing a name (a name that is in the scope must be renamed;
for an example, see move_let_into_expr/2 or any function that calls
sub_subst_scope/1). We also use the scope to optimize sub_del_var/2
and sub_is_val/2.

When optimizing case expressions, the scope could be reset to an
empty list (because sub_new/0 was called instead of sub_new/1).
That could cause name capture if inlining was turned on.

As simple way to force this bug is to uncomment the
"-define(DEBUG, 1)." near the beginning of the file. Without this
correction, most files in the test suite fail to compile.

* egil/fix-doc-links:
  doc: Fix broken links in Installation Guide
  doc: Fix broken links