Issue 4097 - Make JSHydra use SpiderMonkey location from an environment variable if available

utils.py

Index: utils.py
===================================================================
--- a/utils.py
+++ b/utils.py
@@ -22,16 +22,20 @@ JSSHELL_SUPPORTED_PLATFORMS = {
         "i686": "linux-i686",
         "x86_64": "linux-x86_64"
     },
     "darwin": "mac"
 }
 
 
 def ensureJSShell():
+    path = os.environ.get('SPIDERMONKEY_BINARY')
+    if path and os.path.isfile(path):
+        return path
+
     baseDir = os.path.dirname(__file__)
 
     try:
         build = JSSHELL_SUPPORTED_PLATFORMS[sys.platform]
         if isinstance(build, dict):
             build = build[platform.machine()]
     except KeyError:
         raise Exception('Platform %s (%s) not supported by JS shell' % (
@@ -43,17 +47,17 @@ def ensureJSShell():
         os.makedirs(shell_dir)
     if sys.platform == 'win32':
         path = os.path.join(shell_dir, 'js.exe')
     else:
         path = os.path.join(shell_dir, 'js')
 
     if os.path.exists(path):
         return path
-    
+
     with closing(urllib.urlopen(JSSHELL_URL % build)) as response:
         data = response.read()
 
     with zipfile.ZipFile(StringIO(data)) as zip:
         zip.extractall(shell_dir)
 
     if not os.path.exists(path):
         raise Exception('Downloaded package didn\'t contain JS shell executable')