changing default for PATCH_DIST_STRIP to -p1

Hi!

I plan to change the default for PATCH_DIST_STRIP (the setting used
for apply upstream patches downloaded via PATCHFILES) from the current
-p0 to -p1.

I don't remember when I last saw an upstream patch that was just
comparing just plain foo.orig to foo. Most, if not all of them, now
look like e.g. git provides them, i.e. comparing a/foo to b/foo.

I'll check for users of packages that use PATCHFILES but not
PATCH_DIST_STRIP and set it to -p0 there first, so this is just a
heads-up.

Cheers,
 Thomas