allow zero-length const_string_add()

Change-Id: I80e9d7ca83d2a4a86ae05de9fafb6a3da8652e5a
allow zero-length scratch adds as well

(and fix -Werror failing out for overflow issues
with other ways of writing that assert...)

Change-Id: I796844f82fef1f475a134741c3267ea1227bf936
Merge tag '1.0.6' into debian

Change-Id: I320e3ac6431857e4b7c19d894eba2af53519ea6d
varnishkafka (1.0.6-1) trusty-wikimedia; urgency=medium

  * Updated to 1.0.6 for:
    * ddcdace allow zero-length scratch adds as well
    * 8b449cc allow zero-length const_string_add()

 -- Brandon Black <bblack@wikimedia.org>  Mon, 27 Oct 2014 18:16:31 +0000

Change-Id: I9da829e0565ad6ecb310867f46ce17ec8a32c5f4