BATCH_MODE_ONLY_SHELL configuration fails with unixy shells

[Russo, David]

There seems to be a bug in make 3.81 when make is configured with 
BATCH_MODE_ONLY_SHELL enabled.  The problem only occurs when 
BATCH_MODE_ONLY_SHELL is enabled, make determines the shell is "unixy", and a 
recipe has a continuation line.

If make determines that the shell is "unixy", the generated shell script used 
to run a rule containing a continuation character will have one too many '\'s.  
For example, the following makefile fails:

all:
        echo this is\
a test

because the generated "batch" file used to run the echo command above is:

echo this is\\
a test

This results in two commands being executed (by unixy shells); "echo" and "a".  
Clearly not what was intended.

If I'm not mistaken, the fix is quite simple and I've attached a patch to a 
description of the problem here: http://savannah.gnu.org/bugs/?24405.  I'd 
appreciate any review/comments of the bug and the patch.

Thanks,

dave