validate.py: Replace deprecated time.clock() calls (eiffel-community#251

)

time.clock() is deprecated and removed in Python 3.8. It was replaced
by time.process_time() and time.perf_counter() in Python 3.3. Replace
the calls in examples/validate.py with time.perf_counter(). This drops
support for Python 2 so the shebang is adjusted (not that the shebang
is very useful for this non-executable file).

This also fixes what probably was an unintentional buglet; on Linux
time.clock() returned the elapsed CPU time but on Windows it returned
the elapsed time. Since the number was seemingly used to report the
validation progress every five seconds the behavior was only correct
on Windows.

examples/validate.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Copyright 2017 Ericsson AB.
 # For a full list of individual contributors, please see the commit history.
@@ -90,7 +90,7 @@ def validateExamples(examples, schemas, maxExamples, shuffle):
   unchecked = []
 
   numChecked = 0
-  latestReportTime = time.clock()
+  latestReportTime = time.perf_counter()
 
   if shuffle:
     random.shuffle(examples)
@@ -111,9 +111,9 @@ def validateExamples(examples, schemas, maxExamples, shuffle):
       print("Reached limit of " + str(maxExamples) + " examples to validate. Breaking.")
       break
 
-    if time.clock() - latestReportTime > 5:
+    if time.perf_counter() - latestReportTime > 5:
       print("Checked " + str(numChecked) + " / " + str(len(examples)) + " examples.", flush=True)
-      latestReportTime = time.clock()
+      latestReportTime = time.perf_counter()
 
   return failures, unchecked, numberOfSuccessfulValidations