sm,common: Move ksba reader and writer support to common/.
* sm/base64.c: Rename to ... * common/ksba-io-support.c: this. * common/ksba-io-support.h: New. * common/Makefile.am (common_sources): Add new files. * sm/Makefile.am (gpgsm_SOURCES): Remove base64.c
- Signed-off-by: Werner Koch <wk@gnupg.org>