If --debug, then echo (live) all command output to screen

Add '--env VAR VAL' to automatically set evironmentvariables during build.

Add user defines at the top of the SPEC file
  --define foo 'bar %{xxx}'
would add the line:
   %define  foo   bar %{xxx}

If META has 'provides', make sure that we only use provides for the
files we actually install.

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This was written using ideas from cpanspec-1.78.
