common: Clarify use of vars in buffer copy code.
* common/exectool.c (my_error_from_errno): New. (copy_buffer_do_copy): Use separate vars for errno values and gpg-error values for clarity. s/assert/log_assert/. (copy_buffer_flush): Ditto. (gnupg_exec_tool_stream): Use gpg_err_code when testing.
NB: It is surprising that es_write seems not to set ERRNO but only
returns the ERRNO value. Need to check whether this is really the
case.
- Signed-off-by: Werner Koch <wk@gnupg.org>