Catch IllegalArgumentException with Java 8. Workaround for ASM 4.1

This further improves compatibility with Java 8 when using ASM 4.1

More info here md-5/SpecialSource@710ccc64394eb760a8c4831290fbffae673d76a4
Merging two AccessChanges should merge their visibility.

Previously a merge would ignore visibility changes entirely, now
it merges them as in apply.
Merge pull request #17 from Kobata/visibility-upgrade

Merging two AccessChanges should merge their visibility.
messed with some stuff for credentail testing