* added "--bdist-base" option to parameterize where we build
    the RPM (comes from "bdist" by default: "build/bdist.<plat>")
  * simplified/cleaned up some code in 'run()' in the process of
    removing (most) hard-coded directory names
  * if "--spec-only", drop spec file in "dist" rather than "redhat"
    (directory name still hard-coded, though)
  * use 'reinitialize_command()' to fetch the "sdist" object to
    tweak before running "sdist" command
  * use 'self.copy_file()' method rather than 'copy_file()' function
  * cosmetic tweaks to comments, error messages