Two cleanup patches, offshoot from fixing issue 2479.

Someone should look over the second patch. I think all occurrences of error
in Storage.Hashed.Tree are actually violations of preconditions (and thus
should use the bug macro) but I haven't checked this thoroughly.

(The first patch is a no-brainer.)

2 patches for repository http://darcs.net/screened:

patch 40301387fbd327e15ac023222f2d371c31eef38b
Author: Ben Franksen <benjamin.franksen@helmholtz-berlin.de>
Date:   Sun Mar  6 20:16:22 CET 2016
  * move command: fixed punctuation of error messages and added a comment

patch 276deb0ab08e9a386f40e719f5663f7301c9f437
Author: Ben Franksen <benjamin.franksen@helmholtz-berlin.de>
Date:   Sun Mar  6 20:18:55 CET 2016
  * use bug from impossible.h instead of error

Attachments

• move-command_-fixed-punctuation-of-error-messages-and-added-a-comment.dpatch
• patch-preview.txt
• unnamed

* move command: fixed punctuation of error messages and added a comment:
OK (comment/msg patch)

* use bug from impossible.h instead of error (in Storage.Hashed.Tree):
looks good. There remain other uses of 'error' in Storage.Hashed.*
(except Tree) but they can be changed later.

Accepted.