improved check for working pristine-tar related to #901952

Only downgrade tar if pristine-tar does not work and tar is 1.30.  Otherwise
use uscan.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=901952

overlay/usr/bin/gitlab-ci-git-buildpackage

@@ -32,9 +32,13 @@ if [[ $debversion = *-* ]]; then
     git clean -fdx
     git reset --hard
     git fetch --all
+    uscan_download="false"
     if git checkout -B pristine-tar origin/pristine-tar; then
+	orig=$(pristine-tar list| head -1)
 	tar_version=`dpkg -s tar | grep '^Version:'`
-	if [[ $tar_version == "Version: 1.30"* ]]; then
+	if pristine-tar checkout $orig; then
+	    echo "pristine-tar works"
+	elif [[ $tar_version == "Version: 1.30"* ]]; then
 	    echo "WARNING: tar v1.30 breaks pristine-tar when working with commits created by older versions of tar https://bugs.debian.org/901952, downgrading to tar 1.29b-1.1"
 	    printf 'Package: tar\nPin: version 1.30+dfsg-2\nPin-Priority: -1\n' \
 		   > /etc/apt/preferences.d/ban-broken-tar.pref
@@ -42,9 +46,14 @@ if [[ $debversion = *-* ]]; then
 	    wget -q http://deb.debian.org/debian/pool/main/t/tar/tar_1.29b-1.1_amd64.deb
 	    dpkg -i tar_1.29b-1.1_amd64.deb
 	    rm -f tar_1.29b-1.1_amd64.deb
+	else
+	    uscan_download="true"
 	fi
+	rm -f $orig
 	buildpackage_options=--git-pristine-tar
-    else
+    fi
+
+    if [ $uscan_download = "true" ]; then
 	echo "no pristine-tar branch, trying uscan";
 	apt_get_auto_install gnupg2 libwww-perl;
 	uscan --verbose --download-current-version --force-download --rename;