Merge branch 'master' into ng/master

Merge branch 'master' into ng/master

This merge breaks few tests.  They will be adjusted by follow-up patches.

* master: (26 commits)
  tests: remove most uses of the AM_PROG_CC_C_O obsolete macro
  coverage: obsolete macro AM_PROG_CC_C_O should cause no warning nor errors
  INSTALL: update copyright years
  ithreads: use runtime (not configure time) detection of perl threads
  copyright: add few missing copyright notices
  maint: files in PLANS are to be exempted from copyright notice
  maint: consistently honor the UPDATE_COPYRIGHT_YEAR environment variable
  copyright: update some copyright years
  compile: use 'compile' script when "-c -o" is used with losing compilers
  HACKING: suggest more checks before releasing
  tests: can fake a compiler not grasping "-c -o" -- globally in all tests
  sync: update files from upstream with "make fetch"
  typofix: in comments in GNUmakefile
  Rename 'maint/' -> 'maintainer/', for Git's sake
  HACKING: minor typofix
  HACKING: bug-tracker, the PLANS directory, and how to plan "big" changes
  HACKING: rewindable branches should live in the 'experimental/*' namespace
  HACKING: fixlets about git branch rewinding policy
  HACKING: commit messages are not to follow GCS ChangeLog rules too strongly
  HACKING: "detailed explanation" in commit messages is almost mandatory
  ...

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>