Patch to error and fail instead of using all available memory
then crashing to detect the error condition of an unmatched
double quote before the end of a file.

I couldn't get it to show nice error messages, so this may not be
the ideal fix.

A test case for this situation has also been added.

Closes #972

Otherwise they could be copied

Issue #409

Issue #409

Closes #966

This reverts commit ce0f054f.

Like the box unop.

Issue #409

Issue #409

This converts the AST fold into a resource that breaks it's own circular
reference (just a temporary workaround until GC), so that failure during fold
will unwind correctly.

Issue #936

For consistency with other constructs that could not possibly return a
value (say, loops).

It is now 1-based, rather than 0 based. (Seems more natural, and allows 0 to
be used to refer to self and maybe to closure.)

Also allows non-referenced args to be implicitly copied again.

Issue #918

Issue #918

Issue #918

Issue #918

This is needed to fix the second example in issue #919

Closes #919

Closes #920

It is no longer needed.

- Loop bodies and resource constructors aren't allowed to have
  trailing expressions anymore.

- An expression that ends* in a block without trailing expression can
  can not be called, indexed, or subscripted.

- Only expression-statements that end* in a block without trailing
  expression can omit their semicolon.

*) 'Ending in a trailing expression' is defined as being a block or
   construct-ending-in-a-block (if, alt) that either ends in an
   expression itself, or ends in another block-like expression that
   has a trailing expression (by these same rules).

This will be used in the near future to decide what can safely
be done with the returned reference.

Issue #918

tyencode/tydecode still don't know about it. return_ref will be extended to take
arguments anyway.

It will include information about returning by alias.

Closes #575

Closes #890

Closes #764
Closes #891

Blocks (or statements involving blocks) that end in a semicolon are no
longer considered the block-expression of their outer block. This used
to be an expression block, but now is a statement block:

    { if foo { ret 1; } else { ret 10; } }

This helps clear up some ambiguities in our grammar.