slightly shorted Extra-Source-Files via wildcards

According to the cabal documentation, "The reason for providing only a
very limited form of wildcard is to concisely express the common case of
a large number of related files of the same file type without making it
too easy to accidentally include unwanted files". I still find it very
annoying that I can't just say "include everything in src recursively".
don't ship cached files

The testing procedure produces .hs files, which we don't want to include
in the tarball because they are generated files. Oops! What was it that
I read about including directories recursively "making it too easy to
accidentally include unwanted files"?