Fixed compiler errors on sealed ToString functions

3 '.ToString' functions cannot be 'override' due to them being sealed.

i.e.:
/playscript-away3d-core/src/com/adobe/utils/AGALMiniAssembler.as(708,28)
:
error CS0239:
`com.adobe.utils.___Users_administrator_Documents_Code_GitRepos_playscri
pt_away3d_core_src_com_adobe_utils_AGALMiniAssembler_as.OpCode.ToString(
)': cannot override inherited member `_root.Object.ToString()'
because it is sealed