security/clamav-lts: Add new port

* Add Long Term Support release of ClamAV
* Add CONFLICTS_INSTALL to security/clamav
* Add entry to UPDATING that explains
  - Upstream changed their end-of-life policy and LTS release is
    introduced
  - How to switch from regular release (security/clamav) to LTS
    release (security/clamav-lts)

Note about setting PORTEPOCH

In general new port should not set PORTEPOCH. But in this case it
should be set with following reason.

1. Recently upstream changed their end-of-life policy as following.
  - Regular feature release (= 0.xyz.0 release) is released more
    frequently, and life time of each feature release is shortened to
    about 4 months.
  - To compensate for the short lifetime of regular feature release,
    Long Term Support feature release is introduced and its life time
    is about 3 years.
2. First LTS starts with version 0.103.3 and it is same as current
   version of security/clamav.
3. Because of short lifetime of regular feature release, it is
   probable that not a few users of security/clamav want to switch to
   security/clamav-lts after the latter is connected (and the former
   is updated to 0.104.0).
3. For such users the entry is added to UPDATING about how to switch
   from security/clamav to security/clamav-lts. And binary package
   user is suggested to execute
   `pkg set -o security/clamav:security/clamav-lts`. This command
   changes the origin of already installed clamav packages. So user
   can switch to LTS version without reinstalling.
4. But if PORTEPOCH isn't set in security/clamav-lts, binary package
   user who executed above command will notice that version of
   installed package (0.103.3,1) succeeds to current version of
   security/clamav-lts (0.103.3). The situation doesn't change after
   new patch release (0.103.4 for example) is released and it causes
   the problem that installed package isn't properly upgraded with
   `pkg upgrade`.
5. So PORTEPOCH is set in  security/clamav-lts to prevent binary
   package user from suffering from such problem.

1 files changed, 2 insertions, 0 deletions

diff --git a/security/clamav/Makefile b/security/clamav/Makefile
index 6e0336b57503..ad1beb45d440 100644
--- a/security/clamav/Makefile
+++ b/security/clamav/Makefile
@@ -42,6 +42,8 @@ CFLAGS_i386=	-march=i486
 # force to use -lthr until it's not fixed.
 LDFLAGS+=	-lthr
 
+CONFLICTS_INSTALL=	clamav-[0-9]*
+
 SUB_FILES=	pkg-deinstall
 SUB_LIST+=	CHMOD=${CHMOD} \
 		CHOWN=${CHOWN} \