Added script to demonstrate the refcount bug during copy

from https://bugzilla.redhat.com/show_bug.cgi?id=711095

scripts/ticket58.py

@@ -0,0 +1,59 @@
+"""
+A script to reproduce the race condition described in ticket #58
+
+from https://bugzilla.redhat.com/show_bug.cgi?id=711095
+
+Results in the error:
+
+  python: Modules/gcmodule.c:277: visit_decref: Assertion `gc->gc.gc_refs != 0'
+  failed.
+
+on unpatched library.
+"""
+
+import threading
+import gc
+import time
+
+import psycopg2
+from StringIO import StringIO
+
+done = 0
+
+class GCThread(threading.Thread):
+    # A thread that sits in an infinite loop, forcing the garbage collector
+    # to run
+    def run(self):
+        global done
+        while not done:
+            gc.collect()
+            time.sleep(0.1) # give the other thread a chance to run
+
+gc_thread = GCThread()
+
+
+# This assumes a pre-existing db named "test", with:
+#   "CREATE TABLE test (id serial PRIMARY KEY, num integer, data varchar);"
+
+conn = psycopg2.connect("dbname=test user=postgres")
+cur = conn.cursor()
+
+# Start the other thread, running the GC regularly
+gc_thread.start()
+
+# Now do lots of "cursor.copy_from" calls:
+for i in range(1000):
+    f = StringIO("42\tfoo\n74\tbar\n")
+    cur.copy_from(f, 'test', columns=('num', 'data'))
+    # Assuming the other thread gets a chance to run during this call, expect a
+    # build of python (with assertions enabled) to bail out here with:
+    #    python: Modules/gcmodule.c:277: visit_decref: Assertion `gc->gc.gc_refs != 0' failed.
+    
+
+# Terminate the GC thread's loop:
+done = 1
+
+cur.close()
+conn.close()
+
+