core: New helper function _gpgme_strconcat.
* src/conversion.c: Include stdarg.h. (do_strconcat): New. (_gpgme_strconcat): New. * src/util.h: Provide fallback for GPGRT_ATTR_SENTINEL. (_gpgme_strconcat): New with sentinel. * src/w32-util.c (find_program_in_dir): Replace malloc and stpcpy by _gpgme_strconcat. (find_program_at_standard_place): Ditto. (_gpgme_set_default_gpg_name): Ditto. (_gpgme_set_default_gpgconf_name): Ditto. (_gpgme_mkstemp): Ditto. (_gpgme_set_override_inst_dir): Repalce malloc and strcpy by strdup.
The function has been taken from gnupg/common/stringhelp.c and license
changed to LPGLv2.1+. I am the original author of that code.
- Signed-off-by: Werner Koch <wk@gnupg.org>