Added 'Force' parameter to Check CRC32 block

This parameter forces a check of the CRC32 even if the CRC flag in
the header is set to false. This is useful because several satellites
use CRC32 but set the flag to false.

grc/csp_check_crc.xml

@@ -4,7 +4,7 @@
   <key>csp_check_crc</key>
   <category>csp</category>
   <import>import csp</import>
-  <make>csp.check_crc($include_header, $verbose)</make>
+  <make>csp.check_crc($include_header, $verbose, $force)</make>
   <param>
     <name>Include header</name>
     <key>include_header</key>
@@ -33,6 +33,21 @@
     </option>
   </param>
 
+  <param>
+    <name>Force</name>
+    <key>force</key>
+    <value>False</value>
+    <type>bool</type>
+    <option>
+      <name>Yes</name>
+      <key>True</key>
+    </option>
+    <option>
+      <name>No</name>
+      <key>False</key>
+    </option>
+  </param>
+
   <sink>
     <name>in</name>
     <type>message</type>

python/check_crc.py

@@ -39,14 +39,15 @@ class check_crc(gr.basic_block):
     """
     docstring for block check_crc
     """
-    def __init__(self, include_header, verbose):
+    def __init__(self, include_header, verbose, force=False):
         gr.basic_block.__init__(self,
             name="check_crc",
             in_sig=[],
             out_sig=[])
 
         self.include_header = include_header
         self.verbose = verbose
+        self.force = force
 
         self.message_port_register_in(pmt.intern('in'))
         self.set_msg_handler(pmt.intern('in'), self.handle_msg)
@@ -65,7 +66,7 @@ def handle_msg(self, msg_pmt):
             if self.verbose:
                 print e
             return
-        if not header.crc:
+        if not self.force and not header.crc:
             if self.verbose:
                 print "CRC not used"
             self.message_port_pub(pmt.intern('ok'), msg_pmt)