locale.c: Add savepv() to setlocale() returns

locale.c: Add savepv() to setlocale() returns

The next call to setlocale can overwrite the returned value from the
current call, depending on platform.  Therefore, one should save the
results.  I forgot this in commit 39e69e777b8.  Now fixing it.

I also audited locale.c to find any other instances.  There were several
where setlocale() is called without saving, and that return is passed to
a function.  It may work now, but it's dangerous to rely on the function
not getting changed in such a way as to do its own setlocale, expecting
the input parameter to be unchanged.  So save the returns from these as
well, as a precaution.