Security update for exim (important)

This update to exim 4.86.2 fixes the following issues:

• CVE-2016-1531: local privilege escalation for set-uid root exim when
  using ‘perl_startup’ (boo#968844)

Important: Exim now cleans the complete execution environment by default.
This affects Exim and subprocesses such as transports calling other
programs. The following new options are supported to adjust this behaviour:

• keep_environment
• add_environment A warning will be printed upon startup if none of these
  are configured.

Also includes upstream changes, improvements and bug fixes:
* Support for using the system standard CA bundle.
* New expansion items $config_file, $config_dir, containing the file and
directory name of the main configuration file. Also $exim_version.
* New "malware=" support for Avast.
* New "spam=" variant option for Rspamd.
* Assorted options on malware= and spam= scanners.
* A commandline option to write a comment into the logfile.
* A logging option for slow DNS lookups.
* New ${env {<variable>}} expansion.
* A non-SMTP authenticator using information from TLS client
certificates.
* Main option "tls_eccurve" for selecting an Elliptic Curve for TLS.
* Main option "dns_trust_aa" for trusting your local nameserver at the
same level as DNSSEC.