Merge #10019: Fix regression relative to 2.6: add newlines if indent=0

Patch by Amaury Forgeot d'Arc, updated by Sando Tosi.

diff --cc Misc/NEWS
index bfa8f83b327a78c4c78f9e42882bfc5d5903f08d,af3ad9ac9a61730736082f4d42c9bfd30af56598..dd82a0c8cb56dd615a19c975e340214ded4b7203
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -103,12 -53,9 +103,15 @@@ Core and Builtin
  Library
  -------
  
+ - Issue #10019: Fixed regression in json module where an indent of 0 stopped
+   adding newlines and acted instead like 'None'.
+ 
 +- Issue #11186: pydoc ignores a module if its name contains a surrogate
 +  character in the index of modules.
 +
 +- Issue #11815: Use a light-weight SimpleQueue for the result queue in
 +  concurrent.futures.ProcessPoolExecutor.
 +
  - Issue #5162: Treat services like frozen executables to allow child spawning
    from multiprocessing.forking on Windows.