This commit also adds a check to see that all files that
are part of an xi:include also have part of XML_FILES
and vice versa. It also fixes any applications where this
was not true.

One more followup to https://github.com/erlang/otp/pull/1056 and
https://github.com/erlang/otp/pull/1023

This time it's about `/usr/bin/env` and `/bin/cp`:
- `/usr/bin/env` in `diameterc` was used to find the bootstrapped
  `escript` executable. Changed it to exlpicit call to `escript` in
  Makefile.
- `/usr/bin/env` and `/bin/cp` were referenced in documentation
  build/install process. Now full paths to this tools are injected using
  autoconf magic.

OTP-10106
OTP-10107

          environment after a number of bugs are fixed and some features
          are added in the documentation build process.

          - The arity calculation is updated.

          - The module prefix used in the function names for bif's are
            removed in the generated links so the links will look like

            http://www.erlang.org/doc/man/erlang.html#append_element-2

            instead of

            http://www.erlang.org/doc/man/erlang.html#erlang:append_element-2

          - Enhanced the menu positioning in the html documentation when a
            new page is loaded.
          - A number of corrections in the generation of man pages (thanks
            to Sergei Golovan)
          - Moved some man pages to more apropriate sections, pages in
            section 4 moved to 5 and pages in 6 moved to 7.
          - The legal notice is taken from the xml book file so OTP's
            build process can be used for non OTP applications.