Change the way block calls are parsed, mark them as block-calls.

This makes it possible to omit the semicolon after the block, and will
cause the pretty-printer to properly print such calls (if
pretty-printing of blocks wasn't so broken). Block calls (with the
block outside of the parentheses) can now only occur at statement
level, and their value can not be used. When calling a block-style
function that returns a useful value, the block must be put insde the
parentheses.

Issue #1054

src/comp/syntax/ast_util.rs

@@ -163,7 +163,7 @@ fn is_exported(i: ident, m: _mod) -> bool {
 }
 
 pure fn is_call_expr(e: @expr) -> bool {
-    alt e.node { expr_call(_, _) { true } _ { false } }
+    alt e.node { expr_call(_, _, _) { true } _ { false } }
 }
 
 fn is_constraint_arg(e: @expr) -> bool {