connection: check for transaction before attempts to access objects in it

so Haraka doesn't crash
Merge pull request #549 from msimerson/connection

connection: check for transaction before attempts to access objects in i...
smtp_proxy: bug fix, defines an undefined variable
Merge pull request #550 from msimerson/smtpproxy

smtp_proxy: bug fix, defines an undefined variable
Prevent duplicate newlines in bounce message
Fix example and prevent leak FDs
Increase the default open file limit in Upstart script
Fix date format on bounce messages
Fix timeout when processing mail
Merge branch 'master' of github.com:baudehlo/Haraka
dnsbl: use boolean config, use callback to refresh, make tests pass when extra DNSBLs are configured