Testsuite: workaround for ksh bug w.r.t. `${1+"$@"}'

[Stefano Lattarini]

Hello automakers.

While doing more tests on my patch series about zsh xtraces
incompatibilities, I run into a subtle bug of ksh.  This bug is
related to a mishandling of the `${1+"$@"}' expression (occurring
when exactly one empty argument is given), and it breaks the test
script `automake.test'.

This breakage is not a regression introduced by my patch, as it
occurs also in the master branch.

Unfortunately, in master, the code triggering the bug is located in 
`AUTOMAKE_run()', and this function is removed by my patch series. 
Thus writing a new patch against master would be mostly useless if
my zsh-xtrace-incompatibilities patch series is going to be applied,
as a conflict will surely arise.
Thus I decided to write the patch against the private branch I'm
using for the zsh-xtrace series.

I will soon post a minimal testcase illustrating the ksh bug, and
then the patch introducing a workaround for it.

Regards,
   Stefano