common: Add an easy to use DER builder.

* common/tlv-builder.c: New.
* common/tlv.c: Remove stuff only used by GnuPG 1.
(put_tlv_to_membuf, get_tlv_length): Move to ...
* common/tlv-builder.c: here.
* common/tlv.h (tlv_builder_t): New.
--

Such code should actually go into libksba and we will eventually do
that.  However, for now it is easier to keep it here.

Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit 5ea878274e)

- Add coverity meta comment from
  commit a95ddffdcd

common/tlv.c

@@ -32,21 +32,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <assert.h>
-
-#if GNUPG_MAJOR_VERSION == 1
-#define GPG_ERR_EOF               (-1)
-#define GPG_ERR_BAD_BER           (1)  /*G10ERR_GENERAL*/
-#define GPG_ERR_INV_SEXP          (45) /*G10ERR_INV_ARG*/
-typedef int gpg_error_t;
-#define gpg_make_err(x,n) (n)
-#else
 #include <gpg-error.h>
-#endif
+
 
 #include "util.h"
 #include "tlv.h"
 
+
 static const unsigned char *
 do_find_tlv (const unsigned char *buffer, size_t length,
              int tag, size_t *nbytes, int nestlevel)