Merge branch 'refs/heads/t/ONESHELL'

A single patch which instructs the build system to run multi-line
statements in Makefiles in a single shell instance.

Cooking in next for nine months.

* refs/heads/t/ONESHELL:
  build: Use .ONESHELL.

diff --cc Makefile.real
Simple merge

diff --cc NEWS.md
index 7ed78027fc29cf5f681e0d4b00464397ff4e995b,55ef3be947ee76d6b0937b33988b0cd960c0e985..bbe200102627b929907a78ff5a14792cdc45f720
--- 1/NEWS.md
--- 2/NEWS.md
+++ b/NEWS.md
@@@ -1,22 -1,6 +1,24 @@@
  NEWS
  ====
  
 +----------------------------------------------
 +0.6.3 (to be announced) "generalized activity"
 +----------------------------------------------
 +
 +- The ff command now accepts a negative argument to instruct the
 +  virtual streaming system to jump backwards in the current audio
 +  stream. The old syntax (e.g., "ff 30-") is still supported but it
 +  is deprecated and no longer documented. The compatibility code is
 +  sheduled for removal after 0.7.0.
 +- para_afh: New option: --preserve to reset the modification time to
 +  the value of the original file after meta data modification.
 +- Overhaul of the compress filter code. The refined algorithm should
 +  reduce clipping. The meaning of --aggressiveness has changed, see the
 +  updated and extended documentation of the compress filter for details.
 +- Cleanup of the audio format handler code.
++- We now build the tree using the .ONESHELL feature of GNU make,
++  which results in a significant speedup.
 +
  --------------------------------------
  0.6.2 (2018-06-30) "elastic diversity"
  --------------------------------------