Correct silly bug about french option with test whether french has been loaded or not doing `then' case and `else' case in reversed order.
- Enable portability with MSYS bash:
  - do not use '\cp' nor '\rm', but 'command cp' or 'command rm' instead
  - define SHELL variable to /bin/bash so that builtin 'command' is defined
- use '$(MAKE)' instead of 'make' for recursive make, cf. '(make) MAKE Variable' info node
- use './cp2dist' instead of 'cp2dist' so that it will work even when '.' is not in $PATH
- Define variable TEXMF_INSTALL_DIR defined by default to $(HOME)/texmf, so that user can select another installation directory.