install/47812: sysinst source sets fetch should be moved to post-inst config menu

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

>Number:         47812
>Category:       install
>Synopsis:       sysinst source sets fetch should be moved to post-inst config 
>menu
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sat May 11 10:00:01 +0000 2013
>Originator:     Izumi Tsutsui
>Release:        NetBSD 6.1_RC4
>Organization:
>Environment:
System: NetBSD/i386 6.1_RC4
Architecture: i386
Machine: i386 but affects all ports using sysinst
>Description:
This PR is an inquiry of change-request for sysinst (i.e. no patches yet).

Source sets fetch and installation support has been added no January 2012:
http://www.nerv.org/~ryo/netbsd/netbsd/?q=id:20120110T210248Z.e7b773e25cefde5f50668990b9ce1a7b93a89cfe

But source sets menu is shown during binary set installation and
usually install media doesn't contain source sets, so its settings
are a bit confusing, as filed in PR install/45972:
http://gnats.netbsd.org/45972

Now sysinst in 6.0 and later has "post-installation configuration menu"
support:
http://www.nerv.org/~ryo/netbsd/netbsd/?q=id:20120406T234854Z.30c07b08991e0a1073a649e35efa9d1bbb5779c2
and it also includes pkgsrc fetch support.
It is completely separated from NetBSD base set binary installation.

So it's much better to move the existing "source sets installation"
into a part of the post-installation configuration menu.

>How-To-Repeat:
Use sysinst, and try to install both source sets and pkgsrc sources.

>Fix:
Changes should be trivial:
 - Revert the original source fetch menu changes
 - Add source sets installation menu in post-inst config as pkgsrc

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