possible bug: "make dist" does not create ".tarball-version"

[Assaf Gordon]

Hello,

I think this is a bug, but perhaps it's intentional (as a deprecated feature) ?

It seems like "make dist" does not create the file ".tarball-version", which results in 
"./build-aux/git-version-gen" returning UNKNOWN if used in a directory from a tarball (as opposed 
to a directory from a git clone).

This doesn't effect the common use case of "./configure && make", because the version 
string is hard-coded in "configure" .
But if some other script uses "./build-aux/git-version-gen", the returned value 
is UNKNOWN.

The solution, I believe, is either:

1. stop using ".tarball-version" (it is only mentioned in "configure.ac" and 
"GNUmakefile", both cases it is only read, not written).

Or,

2. generate ".tarball-version" (just like "coreutils" does), by adding this line to 
"Makefile.am":
====
dist-hook: gen-ChangeLog
        $(AM_V_GEN)echo $(VERSION) > $(distdir)/.tarball-version
====

Regards,
 -gordon