Update src/main/java/com/icegreen/greenmail/smtp/SmtpManager.java

For some reason, SmtpManager duplicates recipients on messages
Update src/main/java/com/icegreen/greenmail/store/InMemoryStore.java

Avoid ConcurrentModificationException by shallow-copying the folders lists before iteration
Merge pull request #5 from romangarcia/master

Some fixes needed for me, maybe usefull for others