* NEWS: Add interface changes.
* src/Makefile.am (libgpg_error_la_SOURCES): Add b64dec.c.
* src/b64dec.c: New.  Taken from gpgme.  Prefix function names with
_gpgrt_.  Change API a bit, not exposing the structure.
* src/gpg-error.def.in: Export Base64 functions.
* src/gpg-error.vers: Likewise.
* src/visibility.c, src/visibility.h: Likewise.
* src/gpg-error.h.in: Add Base64 struct and functions.
* src/gpgrt-int.h: Add Base64 internal functions.
* tests/Makefile.am (TESTS): Add t-b64dec.
* tests/t-b64dec.c: New.