Introduce Stmt\Block

Stmt\Block will be created for { $a; } style blocks, unless these
occur directly inside some structure that is usually combined
with a block.

For exampl

Introduce Stmt\Block

Stmt\Block will be created for { $a; } style blocks, unless these
occur directly inside some structure that is usually combined
with a block.

For example if ($a) { $b; } will continue to use the old
representation (plain array in in If_::$stmts), but a free-standing
{ $b; } will become a Stmt\Block.

Fixes #590.

show more ...