Replaced the use of CURLOPT_USERPWD for the preferred CURLOPT_USERNAME
and CURLOPT_PASSWORD options and used the same username and password for
all email examples which is the same as that used in the test suite.
These examples show how to fetch a single message (RETR command) and how to
list all the messages in a given mailbox (LIST command), with authentication
via SSL.
They were both based on the https.c example.