RFR(S): 8142386: Octane crashes with assert(is_Load())

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8142386/webrev.00/

There are 2 problems with my recent change to handle mismatched unsafe accesses:

- If the access is compiled as a LoadN+DecodeN then GraphKit::make_load() doesn’t get a load node from LoadNode::make() and can’t set the mismatched flag

- array fields are of type T_ARRAY which differs from T_OBJECT and so are treated as mismatched

Roland.