Bug#432564: Allow debian/rules to not be a makefile

[Ian Jackson <ian@davenant.greenend.org.uk>]

Package: debian-policy
Version: 3.7.2.2

Currently, we have:

  4.9 Main building script: debian/rules

  This file must be an executable makefile, and contains the
  package-specific recipes for compiling the package and building
  binary package(s) from the source.

  It must start with the line #!/usr/bin/make -f, so that it can be
  invoked by saying its name rather than invoking make explicitly.

There is no technical reason why this has to be a makefile.  I propose:

  4.9 Main building script: debian/rules

  This file is normally an executable makefile, and contains the
  package-specific recipes for compiling the package and building
  binary package(s) from the source.

  debian/rules must be an executable script with an appropriate #!
  line (so, if it is a makefile it must start with the line
  #!/usr/bin/make -f) so that it can be invoked by saying its name.
  It should use a widely-used language, and should restrict itself to
  features portable even to older versions of its interpreter.

Ian.