#5116 Allow \change to same context type

[David Kastrup]

Allow \change to same context type

The \change command no longer refuses to change the parent of a
context when the context itself would be of the proper type to
change to. This allows changing the parent of a context that
could be nested, like StaffGroup in StaffGroup or NullVoice
in Staff (since NullVoice is also aliased to Staff).

http://codereview.appspot.com/322820043

[Anonymous]

Passes make, make check and a full make doc.

[David Kastrup]

Add a regtest (proposed by Dan, modified a bit)

http://codereview.appspot.com/322820043

[Anonymous]

Passes make, make check and a full make doc.

[Anonymous]

Patch on countdown for April 12th

[Anonymous]

Patch counted down - please push.

[David Kastrup]

Pushed to staging as
commit 4c1bf39e4a6dd40fec4cea546846e2c721ac5993
Author: David Kastrup dak@gnu.org
Date: Fri Apr 7 10:22:04 2017 +0200

Issue 5116/2: Add regtest

commit 0a5768354b85264bc474baff8752f2c3e205cbe2
Author: David Kastrup dak@gnu.org
Date: Thu Apr 6 09:50:24 2017 +0200

Issue 5116/1: Allow \change to same context type

The \change command no longer refuses to change the parent of a
context when the context itself would be of the proper type to
change to.  This allows changing the parent of a context that
could be nested, like StaffGroup in StaffGroup or NullVoice
in Staff (since NullVoice is also aliased to Staff).