smtp: add the class to verify the certificate of the SMTP server for STARTTLS Original "smtplib.SMTP" has no route to pass "ca_certs" and "cert_reqs" arguments to underlying SSL socket creation. This causes that "getpeercert()" on SSL socket returns empty dict, so the peer certificate for STARTTLS can't be verified. This patch introduces the "STARTTLS" class derived from "smtplib.SMTP" to pass "ca_certs" and "cert_reqs" arguments to underlying SSL socket creation. Almost all code of "starttls()" in this class is imported from "smtplib.SMTP" of Python 2.7.3, but it differs from original code in points below: - "self.ehlo_or_helo_if_needed()" invocation is omitted, because: - "ehlo_or_helo_if_needed()" is available with Python 2.6 or later, and - "ehlo()" is explicitly invoked in "mercurial.mail._smtp()" - "if not _have_ssl:" check is omitted, because: - "_have_ssl" is available with Python 2.6 or later, and - same checking is done in "mercurial.sslutil.ssl_wrap_socket()" - "ssl.wrap_socket()" is replaced by "sslutil.ssl_wrap_socket()" for compatibility between Python versions - use "sock.recv()" also as "sock.read()", if "sock" doesn't have "read()" method with Python 2.5.x or earlier, "sslutil.ssl_wrap_socket()" returns "httplib.FakeSocket"-ed object, and it doesn't have "read()" method, which is invoked via "smtplib.SSLFakeFile".