Merge branch 'ky/imap-send-openssl-1.1.0' into maint

Upcoming OpenSSL 1.1.0 will break compilation b updating a few APIs
we use in imap-send, which has been adjusted for the change.

* ky/imap-send-openssl-1.1.0:
  configure: remove checking for HMAC_CTX_cleanup
  imap-send: avoid deprecated TLSv1_method()
  imap-send: check NULL return of SSL_CTX_new()
  imap-send: use HMAC() function provided by OpenSSL

diff --cc Makefile
Simple merge

diff --cc configure.ac
Simple merge

diff --cc git-compat-util.h
Simple merge

diff --cc imap-send.c
Simple merge