select: Run tests more thoroughly

With more iterations it triggers a bug:

	kirr@deco:~/src/tools/go/pygolang$ py.test -vsx
	============================================== test session starts ===============================================
	platform linux2 -- Python 2.7.15+, pytest-3.6.4, py-1.6.0, pluggy-0.6.0 -- /usr/bin/python2
	cachedir: .pytest_cache
	rootdir: /home/kirr/src/tools/go/pygolang, inifile:
	collected 7 items

	golang/_gopath_test.py::test_import_module PASSED
	golang/_gopath_test.py::test_import_package PASSED
	golang/gcompat_test.py::test_qq PASSED
	golang/golang_test.py::test_go PASSED
	golang/golang_test.py::test_chan PASSED
	golang/golang_test.py::test_select Exception in thread Thread-117:
	Traceback (most recent call last):
	  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
	    self.run()
	  File "/usr/lib/python2.7/threading.py", line 754, in run
	    self.__target(*self.__args, **self.__kwargs)
	  File "/home/kirr/src/tools/go/pygolang/golang/golang_test.py", line 320, in _
	    assert (_, _rx) == (1, 'b')
	AssertionError: assert (1, 'xxx1') == (1, 'b')
	  At index 1 diff: 'xxx1' != 'b'
	  Full diff:
	  - (1, 'xxx1')
	  + (1, 'b')

golang/golang_test.py

@@ -137,6 +137,8 @@ def test_chan():
 
 
 def test_select():
+    N = 1000 # times to do repeated select/chan or select/select interactions
+
     # non-blocking try send: not ok
     ch = chan()
     _, _rx = select(
@@ -172,7 +174,7 @@ def test_select():
         done.close()
     go(_)
 
-    for i in range(10):
+    for i in range(N):
         tdelay()
         _, _rx = select(
                 (ch.send, i),
@@ -186,12 +188,12 @@ def test_select():
     ch = chan()
     done = chan()
     def _():
-        for i in range(10):
+        for i in range(N):
             ch.send(i)
         done.close()
     go(_)
 
-    for i in range(10):
+    for i in range(N):
         tdelay()
         if i % 2:
             _, _rx = select(
@@ -290,7 +292,7 @@ def test_select():
 
     # buffered ping-pong
     ch = chan(1)
-    for i in range(10):
+    for i in range(N):
         _, _rx = select(
             (ch.send, i),
             ch.recv,
@@ -300,7 +302,7 @@ def test_select():
 
 
     # select vs select
-    for i in range(10):
+    for i in range(N):
         ch1 = chan()
         ch2 = chan()
         done = chan()