add test notebook and script for #1260 (GIL-related heartbeat failures)

per  #1127

docs/examples/tests/heartbeat/gilsleep.ipynb

@@ -0,0 +1,56 b''
+{
+ "metadata": {
+  "name": "gilsleep"
+ }, 
+ "nbformat": 2, 
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "markdown", 
+     "source": [
+      "Holding the GIL for too long could disrupt the heartbeat due to non-copying sends.", 
+      "", 
+      "The following cell repeatedly calls a function that holds the GIL for five seconds.", 
+      "", 
+      "The heartbeat will fail after a few iterations prior to fixing Issue [#1260](https://github.com/ipython/ipython/issues/1260)."
+     ]
+    }, 
+    {
+     "cell_type": "code", 
+     "collapsed": false, 
+     "input": [
+      "import sys", 
+      "import time", 
+      "", 
+      "from cython import inline", 
+      "", 
+      "def gilsleep(t):", 
+      "    \"\"\"gil-holding sleep with cython.inline\"\"\"", 
+      "    code = '\\n'.join([", 
+      "        'from posix cimport unistd',", 
+      "        'unistd.sleep(t)',", 
+      "    ])", 
+      "    while True:", 
+      "        inline(code, quiet=True, t=t)", 
+      "        print time.time()", 
+      "        sys.stdout.flush() # this is important", 
+      "", 
+      "gilsleep(5)"
+     ], 
+     "language": "python", 
+     "outputs": [], 
+     "prompt_number": 1
+    }, 
+    {
+     "cell_type": "code", 
+     "collapsed": true, 
+     "input": [], 
+     "language": "python", 
+     "outputs": [], 
+     "prompt_number": " "
+    }
+   ]
+  }
+ ]
+}
  No newline at end of file

docs/examples/tests/heartbeat/hb_gil.py

@@ -0,0 +1,31 b''
+"""
+Run this script in the qtconsole with one of:
+
+    %loadpy hb_gil.py
+
+or
+    %run hb_gil.py
+
+Holding the GIL for too long could disrupt the heartbeat.
+
+See Issue #1260: https://github.com/ipython/ipython/issues/1260
+
+"""
+
+import sys
+import time
+
+from cython import inline
+
+def gilsleep(t):
+    """gil-holding sleep with cython.inline"""
+    code = '\n'.join([
+        'from posix cimport unistd',
+        'unistd.sleep(t)',
+    ])
+    while True:
+        inline(code, quiet=True, t=t)
+        print time.time()
+        sys.stdout.flush() # this is important
+
+gilsleep(5)