* Foreign key support in SQLite is not a persistent setting, so enable

it at startup.
* Implement negative caching.  Now `make check' passes.

tests/referrers.sh

@@ -3,6 +3,8 @@ source common.sh
 # This takes way to long on Cygwin (because process creation is so slow...).
 if test "$system" = i686-cygwin; then exit 0; fi
 
+clearStore
+
 max=2500
 
 reference=$NIX_STORE_DIR/abcdef
@@ -25,34 +27,11 @@ echo "registering..."
 
 time $nixstore --register-validity < $TEST_ROOT/reg_info
 
-oldTime=$(cat test-tmp/db/info/1 | grep Registered-At)
-
-echo "sleeping..."
-
-sleep 2
-
-echo "reregistering..."
-
-time $nixstore --register-validity --reregister < $TEST_ROOT/reg_info
-
-newTime=$(cat test-tmp/db/info/1 | grep Registered-At)
-
-if test "$newTime" != "$oldTime"; then
-    echo "reregistration changed original registration time"
-    exit 1
-fi
-
-if test "$(cat test-tmp/db/referrer/1 | wc -w)" -ne 1; then
-    echo "reregistration duplicated referrers"
-    exit 1
-fi
-
 echo "collecting garbage..."
 ln -sfn $reference "$NIX_STATE_DIR"/gcroots/ref
 time $nixstore --gc
 
-if test "$(cat test-tmp/db/referrer/abcdef | wc -w)" -ne 0; then
+if test "$(sqlite3 ./test-tmp/db/db.sqlite 'select count(*) from Refs')" -ne 0; then
     echo "referrers not cleaned up"
     exit 1
 fi
-