Test largest valid initial size for memory32 in memory.wast (WebAssembly#105)

* Test largest valid initial size for memory32 in memory.wast

* Only validate and don't instantiate large memory

Author: evicy

test/core/memory.wast

@@ -5,6 +5,7 @@
 (module (memory 0 0))
 (module (memory 0 1))
 (module (memory 1 256))
+(module definition (memory 65536))
 (module (memory 0 65536))
 
 (module (memory (data)) (func (export "memsize") (result i32) (memory.size)))