Change `read_string` to fail when not the entire input has been
consumed. This avoids unexpected, even dangerous behavior (fixes#6223).
The new JSON parser adapted in #6121 also solves this problem so in
master this is a temporary fix, but should be backported to older releases.
Also adds tests for the new behavior.
Github-Pull: #6226
Rebased-From: 4e157fc60d
there is no internal modification of any file in this commit
files are moved into directories according to established standards in
sourcecode distribution; these directories contain:
src - Files that are used in constructing the executable binaries,
but are not installed.
doc - Files in HTML and text format that document usage, quirks of
the implementation, and contributor checklists.
locale - Files that contain human language translation of strings
used in the program
contrib - Files contributed from distributions or other third party
implementing scripts and auxiliary programs