[GH #813 + #814] Fix MIME/Base64.pir for encoded strings
[GH #813 + #814] Fix MIME/Base64.pir for encoded strings

Use bytebuffer representations of the encoded string, not the encoded ord value.
Now the implementation is correct, but some encoded tests not.

FROGGS/parrot,FROGGS/parrot,FROGGS/parrot,FROGGS/parrot,tkob/parrot,FROGGS/parrot,parrot/parrot,youprofit/parrot,parrot/parrot,parrot/parrot,FROGGS/parrot,FROGGS/parrot,youprofit/parrot,tkob/parrot,youprofit/parrot,tkob/parrot,tkob/parrot,tkob/parrot,parrot/parrot,tkob/parrot,tkob/parrot,youprofit/parrot,parrot/parrot,tkob/parrot,youprofit/parrot,youprofit/parrot,youprofit/parrot,FROGGS/parrot,youprofit/parrot