[tlbuild] How to install a Perl script

[Andreas Scherer]

Dear TL experts,

I would like to add the Perl script 'proofsort' 
(https://www.tug.org/svn/texlive/trunk/Build/source/texk/web2c/cwebdir/proofsort?revision=67353&view=markup) 
to the present CWEB binaries. Unfortunately, I am totally unfamiliar 
with the necessary steps to add this to cweb.am, Makefile.am, and 
Makefile.in.

To make this Perl script match the other CWEB tools, it should also be 
renamed to 'ctwill-proofsort' (cf. 'ctwill-refsort') when installed.

Thanks for your help,
Andreas