* lib/net/smtp.rb: new exception class SMTPError.
* lib/net/smtp.rb: new exception class SMTPAuthenticationError.
* lib/net/smtp.rb: new exception class SMTPServerBusy.
* lib/net/smtp.rb: new exception class SMTPSyntaxError.
* lib/net/smtp.rb: new exception class SMTPFatalError.
* lib/net/smtp.rb: new exception class SMTPUnknownError.
* lib/net/smtp.rb: change critical section protect algorithm.
* lib/net/smtp.rb (SMTP#do_start): check authentication args before all.
* lib/net/smtp.rb: new method send_message (alias send_mail).
* lib/net/smtp.rb: new method open_message_stream (alias ready).
* lib/net/pop.rb: POPBadResponse is a POPError.
* lib/net/pop.rb (POPMail#pop): ban ReadAdapter.
* lib/net/pop.rb (POPMail#top): ditto.
* lib/net/pop.rb (POP3Command): change critical section protect algorithm.
* lib/net/pop.rb (POP3Command#auth): USER and PASS should be one critical block.
* lib/net/pop.rb (POP3Command#retr): ban `dest' argument using iterator.
* lib/net/pop.rb (POP3Command#top): ditto.
* lib/net/protocol.rb: #read_message_to -> #each_message_chunk
* lib/net/protocol.rb: #D -> #LOG
* lib/net/protocol.rb: #D_off -> #LOG_off
* lib/net/protocol.rb: #D_on -> #LOG_on


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4026 b2dd03c8-39d4-4d8f-98ff-823fe69b080e