add test for prev release

tests/get_ver.spec

+Name: get_version_test
+Version: 2.1
+Release: alt0
+Summary: Test
+Group: Other
+License: Public License
+
+%description
+Get version test

tests/test_prevprelease.sh

+#!/bin/sh
+
+. `dirname $0`/../share/eterbuild/functions/common
+load_mod spec
+
+SPECNAME=get_ver.spec
+
+check()
+{
+	[ "$2" != "$3" ] && echo "FATAL with '$1': result '$3' do not match with '$2'" || echo "OK for '$1' with '$2'"
+}
+
+fill_spec()
+{
+cat <<EOF >$SPECNAME
+Name: get_version_test
+Version: 2.1
+Release: $RELEASE
+Summary: Test
+Group: Other
+License: Public License
+
+%description
+Get version test
+EOF
+}
+
+check_prev()
+{
+	# from rpmbh:
+	# General rule: always alt(N-1).MM.(N)
+	RELEASE="$2"
+	fill_spec
+	RELEASE=$(get_release $SPECNAME)
+	test -n "$RELEASE" || fatal "release missed"
+	BASERELEASE=$(get_numrelease $SPECNAME)
+	test -n "$BASERELEASE" || fatal "baserelease missed"
+	local RES="$(get_txtrelease $SPECNAME)$(decrement_release $BASERELEASE).$MDISTR.$BASERELEASE"
+	check "$2" "$1" "$RES"
+}
+
+MDISTR=M40
+check_prev alt2.M40.3 alt3
+check_prev alt2.M40.3.r201.2 alt3.r201.2
+check_prev alt0.M40.1 alt1
+check_prev alt0.M40.0 alt0
+
+#rm -f $SPECNAME