Add --enable-download option to check-configure

[d-torrance]

During configure, we raise an error if the input for --enable-download is "yes" but neither wget nor curl are available on the system.

Now that the default for --enable-download is "yes", we should make sure that we don't raise this error during check-configure if the user initially ran configure with "no", e.g., in Debian/Ubuntu package builds.