When decoding, always allow newlines in input, with almost no
performance impact.
* src/base64.c (do_decode): Initialize decode context.
Call base64_decode one more time, after all input is processed.
(usage): When decoding, newlines are always accepted.
* tests/misc/base64: Add a bunch of tests, for the above.
* gl/lib/base64.c: Include <string.h>.
(base64_decode_ctx_init, get_4, decode_4): New functions.
(base64_decode): Efficiently handle interspersed newlines.
(base64_decode_alloc): Update signature.
* gl/lib/base64.h (struct base64_decode_context): Define.
(base64_decode_ctx_init): Add prototype.
(base64_decode, base64_decode_alloc): Update prototypes.
[doc/ChangeLog]
* coreutils.texi (base64 invocation): When decoding, newlines
are always accepted.
