Test circular reference detection. Very basic examples from NASM's docs on

critical expressions.
NASM behavior: 1-3 fail, 4 generates a 4-byte offset in the memory expression.
YASM behavior: 1&2 fail (and rightfully so :), 3 works as expected, and 4
 generates a 1-byte offset.

svn path=/trunk/yasm/; revision=473

tests/nasm/circular1.asm

@@ -0,0 +1,2 @@
+	times (label-$) db 0
+label:	db 'Where am I?'

tests/nasm/circular2.asm

@@ -0,0 +1,2 @@
+	times (label-$+1) db 0
+label:	db 'NOW where am I?'

tests/nasm/circular3.asm

@@ -0,0 +1,3 @@
+	mov ax, symbol1
+symbol1 equ symbol2
+symbol2:

tests/nasm/circular4.asm

@@ -0,0 +1,2 @@
+	mov eax, [ebx+offset]
+offset equ 10