DO NOT buffer base64 encoded attachments before we decode them. Instead

DO NOT buffer base64 encoded attachments before we decode them. Instead
decode them directly after we retrieved the data from the imapserver and
echo te result. This will safe a lot of memmory usage :)

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@5078 7612ce4b-ef26-0410-bec9-ea0150e637f0