apply-patches.sh: Go back to only warn about unsupported file types

Fixes http://autobuild.buildroot.net/results/868/8687be8ec029486d9c5e2224cde542134f72884b/



The recent (d245fbb4: apply-patches.sh: detect missing patches)
change to apply-patches.sh causes a number of regressions with packages
using downloadable tarballs of patches (typically from Debian), as
those contain additional files besides just the patches (ChangeLog's,
debian/rules, ..).

This use case is arguably abusing the _PATCH handling, but it used to
work so people might rely on it so go back to only warn about this
instead of erroring out.

At the same time reword the warning message.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>