qpkg: test for the QPKG_ADDING leakage bug

- test/bug-adding: test if we get a false cyclic dependency because
  QPKG_ADDING isn't properly removed
- TODO: mention the problem

qpkg/test/bug-adding

@@ -0,0 +1,44 @@
+#!/bin/sh
+. ./Common
+
+###############################################################################
+
+#
+# See the comment at the end of "resolve" in prereq.c for details.
+#
+
+qpkg_fail "BUG: we don't clean up QPKG_ADDING, yielding false errors" \
+  prereq A <<EOF
+Package: D
+Version: 0
+Architecture: test
+Conflicts: B (= 1)
+Filename: D_0
+
+Package: C
+Version: 0
+Architecture: test
+Depends: D
+Filename: C_0
+
+Package: B
+Version: 1
+Architecture: test
+Depends: C
+Filename: B_1
+
+Package: B
+Version: 0
+Architecture: test
+Depends: C
+Filename: B_0
+
+Package: A
+Version: 0
+Architecture: test
+Depends: B
+Filename: A_0
+EOF
+expect <<EOF
+package C version 0 has cyclic dependency
+EOF