Generating the Patch files for MacPort

1) Why
  MacPorts uses "configure" to generate its current Makefiles and/or installation
  scripts from the generic ones with the appropriate compiler version and
  compilation switches
  
  Imager (as Gildas) did that in a different way
  
  Thus, the explicit names of compiler and explicit switches in some Makefile.*
  or *.sh in admin/ must be replaced by the usual "configure" symbols, e.g.
    @CC@ for  cc
    @PYTHON@ for Python
  etc..
  
  see the "configure" section in the Portfile.txt for a complete list
  
2) Unfortunately, there is no automatic way to generate the patch files for MacPorts
  This has to be done by manually editing the relevant files to do this "by hand"
  
  As a result, any modification in these files is dangerous, and may require
  a similar change in the .diff patch file
  
3) Verifying the patch files

  $ cd MacPorts
  $ cp ../admin/(file)
  $ patch < patch-admin-(file).diff
  
  A) If it works, then the patch is still valid.
  B) If not, it must be either edited (usually a small change of line numbers
      by a couple of units, rarely more), 
  C) or, in more complex cases, it must be re-created. See instructions below
      A good way to generate the modified patched file is to generate a patch 
      file from the Git repository for the changes in the original file version, 
      and apply this patch to the local patched copy of the file (because the
      2 patches at stake are independent).
  D) Ultimately, one may even simply handle that through a MacPorts branch ??
  
4) MacPort uses a relative path structure and the first 2 lines of the .diff patch
  files to figure out on which files the patch applies. 
  
  Thus, the patch should be generated by
    $ diff -u 
  from 1 directory atop the admin/ directory (in order to allow simple versioning)
  and the -p1 flag is used by "patch", through the appropriate switch in the 
  Portfile.txt
  
5) List of patch files

patch-admin-Makefile.build.diff
patch-admin-Makefile.def.diff
patch-admin-Makefile.python.diff
patch-admin-define-system.sh.diff
patch-admin-imager-env.sh.diff
