Fix mismatch descriptor and signature found for function pointer

[Henry Jen]

Hi,

Please review the webrev[1] that,

- Only change Pointer signature for TypeAlias for Pointer type. This bug is causing mismatch of function descriptor and signature when a typedef callback is used as a function parameter.
- Minor tweak for test/debug

Cheers,
Henry

[1] http://cr.openjdk.java.net/~henryjen/panama/foreign/FISignature/webrev/