Allow SSL to be used when a new config setting, imap.ssl, is set to
true.

Also, automatically use TLS when imap.ssl is not set by using the IMAP
STARTTLS command, if the server supports it.

Tested with Courier and Gimap IMAP servers.

Signed-off-by: Robert Shearman <robertshearman@gmail.com>
---
 Documentation/git-imap-send.txt |    1 +
 Makefile                        |    4 +-
 imap-send.c                     |  163
+++++++++++++++++++++++++++++++++++---- 3 files changed, 152
insertions(+), 16 deletions(-)