Fixed setup.py for tclsh check.

setup.py

@@ -91,8 +91,8 @@ class BuildExtWithoutPlatformSuffix(build_ext):
         return get_ext_filename_without_platform_suffix(filename)
 
 def check_tcl_version():
-    output = subprocess.check_output("echo \"puts \$tcl_version;exit 0\" | tclsh", shell=True)
     try:
+        output = subprocess.check_output("echo \"puts \$tcl_version;exit 0\" | tclsh", shell=True)
         val = float(output)
     except (TypeError,ValueError):
         val = None