start of tests refactoring; sqlite3 new wrapper fixes

tests/accept/compile/tobjcov.nim

@@ -0,0 +1,17 @@
+# Covariance is not type safe:
+
+type
+  TA = object
+    a: int
+  TB = object of TA
+    b: array[0..5000_000, int]
+    
+proc ap(x: var TA) = x.a = -1
+proc bp(x: var TB) = x.b[high(x.b)] = -1
+    
+# in Nimrod proc (x: TB) is compatible to proc (x: TA),
+# but this is not type safe:
+var f: proc (x: var TA) = bp
+var a: TA
+f(a) # bp expects a TB, but gets a TA
+