Fix sed script for package name uniqueness

Until now, the sed script for determining URL download rules in reproduce/software/make/high-level.mk considered package names such as fftw-3... and fftw2-2.1... to be identical. Given that some researchers may not immediately have time to update and contribute changes upstream to all the packages that they depend on, there are situations were they may wish to use both package simultaneously. Moreover, it would be unwise for them to remove well-established packages from the high-level.mk elif list of download URLs, even though the user should, in principle, check this list to decide if s/he accepts those particular URLs to be trustable.

With this commit, the sed script considers fftw-3... and fftw-2... to be identical, but fftw-3-... and fftw2-2.1... to be different. The older algorithm worked on single characters; the new one works on the first pair of characters satisfying the new rule, since the awk selects only the first word.