Use RPMTAG_RPMFORMAT for rpm format detection in the signing code

We now have a nice way to centrally get the format number, use it
in the signing code instead of the various ad-hoc methods added during
multi-signature development, and use 'rpmformat' as the variable name
for easy grepping.

No functional changes.

sign/rpmgensig.cc

@@ -641,7 +641,8 @@ static int rpmSign(const char *rpm, int deleting, int flags)
     struct sigTarget_s sigt_v4;
     unsigned int origSigSize;
     int insSig = 0;
-    rpmTagVal reserveTag = RPMSIGTAG_RESERVEDSPACE;
+    int rpmformat = 0;
+    rpmTagVal reserveTag = 0;
 
     if (manageFile(&fd, rpm, O_RDWR))
 	goto exit;
@@ -671,7 +672,9 @@ static int rpmSign(const char *rpm, int deleting, int flags)
 	goto exit;
     }
 
-    if (!headerIsEntry(h, RPMTAG_HEADERIMMUTABLE)) {
+    rpmformat = headerGetNumber(h, RPMTAG_RPMFORMAT);
+
+    if (rpmformat < 4) {
 	rpmlog(RPMLOG_ERR, _("Cannot sign RPM v3 packages: %s\n"), rpm);
 	goto exit;
     }
@@ -682,8 +685,7 @@ static int rpmSign(const char *rpm, int deleting, int flags)
 	flags |= RPMSIGN_FLAG_RPMV3;
     }
 
-    /* Only v6 packages have this */
-    if (headerIsEntry(sigh, RPMSIGTAG_RESERVED)) {
+    if (rpmformat >= 6) {
 	flags |= RPMSIGN_FLAG_RPMV6;
 	reserveTag = RPMSIGTAG_RESERVED;
 	/* v3 signatures are not welcome in v6 packages */
@@ -694,6 +696,7 @@ static int rpmSign(const char *rpm, int deleting, int flags)
 	}
     } else {
 	flags |= RPMSIGN_FLAG_RPMV4;
+	reserveTag = RPMSIGTAG_RESERVEDSPACE;
 	/* Ensure only one legacy signature is added if adding v6 signatures */
 	if ((flags & RPMSIGN_FLAG_RPMV6) && haveLegacySig(sigh))
 	    flags &= ~(RPMSIGN_FLAG_RPMV4|RPMSIGN_FLAG_RPMV3);