Remove the __log function for __log_level

Also redefine all of the standard logging macros to use more rust code instead
of custom LLVM translation code. This makes them a bit easier to understand, but
also more flexibile for future types of logging.

Additionally, this commit removes the LogType language item in preparation for
changing how logging is performed.

src/libsyntax/ast.rs

@@ -505,7 +505,9 @@ pub enum Expr_ {
     ExprBreak(Option<Ident>),
     ExprAgain(Option<Ident>),
     ExprRet(Option<@Expr>),
-    ExprLog(@Expr, @Expr),
+
+    /// Gets the log level for the enclosing module
+    ExprLogLevel,
 
     ExprInlineAsm(inline_asm),