This change allows qualified references to local labels from other
sections: you can do `#send section.local` and it will take you to the
appropriate `:.local` label. When `section.local` is ambiguous due to
sections/locals sharing the same names, the reference resolves to the
local in the first such section.
This changes the semantics of local labels. Previously, local labels
were just shorthand for writing out `name.local`, which meant if there
were multiple sections named "name", there could potentially be name
collisions.
This commit adds a unique numeric suffix to each section's ID string.
This guarantees that locals in one section won't interfere with those in
a different section.