Support FIPS mode where possible

Computer systems can be configured to operate in compliance with the U.S.
Federal Information Processing Standards. Such configuration restricts usage of
MD5 due to its cryptographic insecurity. Trying to use `hashlib.md5()` on a FIPS
system raises an exception:

```
ValueError: [digital envelope routines: EVP_DigestInit_ex] disabled for FIPS
```

In Python 3.9 and newer, using MD5 for non-cryptographic purposes is allowed by
passing `usedforsecurity=False`.

cogapp/cogapp.py

@@ -2,6 +2,7 @@
 """
 
 import copy
+import functools
 import getopt
 import glob
 import hashlib
@@ -57,6 +58,13 @@
     -h          Print this help.
 """
 
+# Support FIPS mode where possible (Python >= 3.9). We don't use MD5 for security.
+md5 = (
+    functools.partial(hashlib.md5, usedforsecurity=False)
+    if sys.version_info >= (3, 9)
+    else hashlib.md5
+)
+
 class CogError(Exception):
     """ Any exception raised by Cog.
     """
@@ -446,7 +454,7 @@ def processFile(self, fIn, fOut, fname=None, globals=None):
 
             self.cogmodule.inFile = sFileIn
             self.cogmodule.outFile = sFileOut
-            self.cogmodulename = 'cog_' + hashlib.md5(sFileOut.encode()).hexdigest()
+            self.cogmodulename = 'cog_' + md5(sFileOut.encode()).hexdigest()
             sys.modules[self.cogmodulename] = self.cogmodule
             # if "import cog" explicitly done in code by user, note threading will cause clashes.
             sys.modules['cog'] = self.cogmodule
@@ -536,7 +544,7 @@ def processFile(self, fIn, fOut, fname=None, globals=None):
                 # Eat all the lines in the output section.  While reading past
                 # them, compute the md5 hash of the old output.
                 previous = ""
-                hasher = hashlib.md5()
+                hasher = md5()
                 while l and not self.isEndOutputLine(l):
                     if self.isBeginSpecLine(l):
                         raise CogError(
@@ -568,7 +576,7 @@ def processFile(self, fIn, fOut, fname=None, globals=None):
 
                 # Write the output of the spec to be the new output if we're
                 # supposed to generate code.
-                hasher = hashlib.md5()
+                hasher = md5()
                 if not self.options.bNoGenerate:
                     sFile = f"<cog {sFileIn}:{firstLineNum}>"
                     sGen = gen.evaluate(cog=self, globals=globals, fname=sFile)