Refactor optional imports, make 'resource' optional.

Ticket #2: https://github.com/kanaka/websockify/issues/2 - win32
support. The 'resource' module is not available under Windows. We only
use it for daemonizing so make it optional and disable daemonizing
support on Windows for now.

Also, refactor how the optional imports to turn them into data instead
of code and iterate through them.

Add early warnings to indicate when modules are missing and
functionality is disabled.

websocket.py

@@ -16,8 +16,7 @@ as taken from http://docs.python.org/dev/library/ssl.html#certificates
 
 '''
 
-import sys, socket, struct, traceback, select
-import os, resource, errno, signal # daemonizing
+import os, sys, errno, signal, socket, struct, traceback, select
 from cgi import parse_qsl
 from base64 import b64encode, b64decode
 
@@ -49,16 +48,16 @@ else:
     from sha import sha as sha1
 
 # Degraded functionality if these imports are missing
-try:
-    # Required for HyBi encode/decode
-    import numpy, ctypes
-except ImportError:
-    numpy = ctypes = None
+for mod, sup in [('numpy', 'HyBi protocol'),
+        ('ctypes', 'HyBi protocol'), ('ssl', 'TLS/SSL/wss'),
+        ('resource', 'daemonizing')]:
+    try:
+        globals()[mod] = __import__(mod)
+    except ImportError:
+        globals()[mod] = None
+        print("WARNING: no '%s' module, %s support disabled" % (
+            mod, sup))
 
-try:
-    import ssl
-except:
-    ssl = None
 
 class WebSocketServer(object):
     """
@@ -98,6 +97,7 @@ Sec-WebSocket-Accept: %s\r
         self.listen_port = listen_port
         self.ssl_only    = ssl_only
         self.daemon      = daemon
+        self.handler_id  = 1
 
         # Make paths settings absolute
         self.cert = os.path.abspath(cert)
@@ -112,16 +112,19 @@ Sec-WebSocket-Accept: %s\r
         if self.web:
             os.chdir(self.web)
 
-        self.handler_id  = 1
+        # Sanity checks
+        if ssl and self.ssl_only:
+            raise Exception("No 'ssl' module and SSL-only specified")
+        if self.daemon and not resource:
+            raise Exception("Module 'resource' required to daemonize")
 
+        # Show configuration
         print("WebSocket server settings:")
         print("  - Listen on %s:%s" % (
                 self.listen_host, self.listen_port))
         print("  - Flash security policy server")
         if self.web:
             print("  - Web server")
-        if ssl and self.ssl_only:
-            raise Exception("No 'ssl' module and SSL only specified")
         if ssl:
             if os.path.exists(self.cert):
                 print("  - SSL/TLS support")