Fix for Makefile.in invoking xref_mod_app.escript

[Boris Mühmer]

This fix modifies "Makefile.in" in such a way, that the target mod2app
doesn't invoke the Erlang script "xref_mod_app.escript" using the
program "env", but instead uses the local "escript" program for the
call.

The reason for the fix is, that either "env" can't find
"escript" (Erlang isn't installed, or is at a location where it can't be
found) or an outdated version of escript might be called.

And here it is:

git fetch git://github.com/bsmr/otp.git fix_makefile_in_for_xref_mod_app_escript


Besides, sorry for the long name.


  - boris