* lib/quotearg.h (quotearg_n, quotearg_n_style):

* lib/quotearg.h (quotearg_n, quotearg_n_style):
First arg is int, not unsigned.
* lib/quotearg.c (quotearg_n, quotearg_n_style): Likewise.
(SIZE_MAX, UINT_MAX): New macros.
(quotearg_n_options): Abort if N is negative.
Avoid overflow check on hosts where size_t is 64 bits and int
is 32 bits, as overflow is impossible there.
Fix off-by-one typo that caused unnecessary reallocation.