Get rid of assumptions about ".nexe" extension.

tests/callingconv/nacl.scons

 # -*- python -*-
 # Copyright 2011 The Native Client Authors.  All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 Import('env')
 
 # If this test is failing on the bots, you can find the seed
 # from the output of the bot. Look for "--seed=".
 # To reproduce the exact problem, set settings['seed'] below
@@ skipping 89 matching lines @@
   j = (j+1) % len(envlist)
 
 # Create the module component objects
 modules = []
 for i in xrange(num_modules):
   modules.append(module_env[i].ComponentObject(nodes[i+1]))
 
 # Compile callingconv.c
 callingconv = link_env.ComponentObject('callingconv.c')
 
-prog = link_env.ComponentProgram('callingconv.nexe',
+prog = link_env.ComponentProgram('callingconv',
                                  [callingconv] + modules)
 
 node = link_env.CommandSelLdrTestNacl(
          'callingconv.out',
-         command=[prog],
+         prog,
          stdout_golden=nodes[0])
 
 env.AddNodeToTestSuite(node, ['medium_tests'], 'run_callingconv_test',
                        # This test takes too long to compile for ARM
                        # and the resulting code doesn't pass this test.
                        is_broken=env.Bit('target_arm'))