Add support for "freebsd-update -r newrelease upgrade" -- binary

upgrading to new releases.  Important parts of this code include
 * automatically determining which optional components (e.g., src,
info, proflibs) are installed.
 * merging changes in files which are modified locally and have
changed between the currently running and new release.
 * prompting the user to rebuild all 3rd party software before
deleting old shared libraries.

Yes, this is compatible with "freebsd-update rollback" -- you can
test a new -BETA and roll back to the old release if you don't
like it.

Subject to re@ approval, this will be MFCed before 7.0-BETA3 and
6.3-RC1.

MFC after:	2 days

1 files changed, 11 insertions, 1 deletions

diff --git a/etc/freebsd-update.conf b/etc/freebsd-update.conf
index 7a3055ca92b6..7f634b2c71c1 100644
--- a/etc/freebsd-update.conf
+++ b/etc/freebsd-update.conf
@@ -23,9 +23,13 @@ IgnorePaths
 
 # Paths which start with anything matching an entry in an UpdateIfUnmodified
 # statement will only be updated if the contents of the file have not been
-# modified by the user.
+# modified by the user (unless changes are merged; see below).
 UpdateIfUnmodified /etc/ /var/
 
+# When upgrading to a new FreeBSD release, files which match MergeChanges
+# will have any local changes merged into the version from the new release.
+MergeChanges /etc/ /var/named/etc/
+
 ### Default configuration options:
 
 # Directory in which to store downloaded updates and temporary
@@ -46,3 +50,9 @@ UpdateIfUnmodified /etc/ /var/
 # FreeBSD Update retain this modified metadata when installing a new version
 # of that file?
 # KeepModifiedMetadata yes
+
+# When upgrading between releases, should the list of Components be
+# read strictly (StrictComponents yes) or merely as a list of components
+# which *might* be installed of which FreeBSD Update should figure out
+# which actually are installed and upgrade those (StrictComponents no)?
+# StrictComponents no