dist: do not wrap calls to 'tar' with the 'missing' script

dist: do not wrap calls to 'tar' with the 'missing' script

The `missing' script is meant to allow non-developers to build a
package in the face of slightly-skewed timestamps (as might happen
e.g. when the package is obtained from a VCS checkout rather than
from a distribution tarball).  It is *not* the business of the
`missing' script to try to provide wrappers for all the maintainer
tools (in this case, to tool being a decent tar program).  Such
wrapping of `tar' was not only inappropriate, but it was also
preventing the legitimate overriding (at make runtime) of the
`tar' program used in the creation of the distribution tarballs.

See also automake bug#9822.

* lib/missing: Don't try to specially wrap `tar' invocations
anymore.
* m4/tar.m4 (_AM_PROG_TAR): In the definitions of the `AMTAR'
variable, do not wrap the `tar' invocation with the `missing'
script anymore.  Instead, allow the user to override the intended
tar program at make runtime, by defining the `TAR' environment
variable.
[$1 == v7]: Similarly for the definitions of the `am__tar' and
`am__untar' variables.  Since we are at it, don't make them depend
anymore on the definition of the obsolescent `AMTAR' variable.
* NEWS: Update.
* tests/missing-tar.test: Remove, it's obsolete.
* tests/tar-override.test: New test.
* tests/Makefile.am (TESTS): Update.

Reported by Akim Demaille.