Rename org-reveal to ox-reveal, matching repo contents
Refuse to build single-file packages where source file name mismatches

If a package is called "foo", but contains only "bar.el", then the
package is arguably broken: the result will be a "foo.el" with the
contents of "bar".

This commit detects that situation and fails the package build.

/cc @milkypostman -- let's see what this breaks.