added Z3_enable_trace/Z3_disable_trace to the Z3 API (these APIs are NOOPs if tracing is not enabled during compilation)

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/bindings/python/z3.py

@@ -37,13 +37,18 @@ Z3 exceptions:
 ...   print "failed:", ex
 failed: 'sort mismatch'
 """
-
 from z3core import *
 from z3types import *
 from z3consts import *
 from z3printer import *
 import io
 
+def enable_trace(msg):
+    Z3_enable_trace(msg)
+
+def disable_trace(msg):
+    Z3_disable_trace(msg)
+
 # We use _z3_assert instead of the assert command because we want to
 # produce nice error messages in Z3Py at rise4fun.com
 def _z3_assert(cond, msg):