sv.h: Add comment

There was recent confusion about this.
locale.c: Handle case where LC_ALL isn't "all"

Setting the LC_ALL locale category on NetBSD does not necessarily change
all the categories to the requested locale.  Sometimes the LC_COLLATE
category is set to POSIX.  I presume that is because collation has not
been defined for the given locale, so it uses a basic locale instead.
The code in locale.c that does locale initialization for the Perl
program at start-up, depended on LC_ALL setting all categories to the
same locale.
t/run/locale.t: Fix skip count

This skipped the wrong number of tests on platforms that don't have a
locale whose decimal radix character isn't a dot.  (e.g. no locales with
a comma).