Use paramWordSize instead of getParamWordSize()

[hrj]

for consistency with invokestatic_fast.

Closes #438

Apart from unit tests, I have tested this with:

• a custom nashorn benchmark
• scimark2
• javac compilation (via javax.tools).

[hrj]

Just FYI, I tested this with a scala program as well. I think Scala uses a lot of reflection during bootstrap.

[jvilk]

Thanks!