Invoke config.py instead of config.pl

git grep -Fl /config.pl | xargs sed -i -e 's!/config\.pl!/config.py!g'

Also:
* Change one comment in include/mbedtls/check_config.h.
* Change PERL to PYTHON in CMakeLists.txt.
diff --git a/tests/scripts/depends-pkalgs.pl b/tests/scripts/depends-pkalgs.pl
index 72c7f41..70e77b0 100755
--- a/tests/scripts/depends-pkalgs.pl
+++ b/tests/scripts/depends-pkalgs.pl
@@ -60,10 +60,10 @@
     print "* Testing without alg: $alg\n";
     print "******************************************\n";
 
-    system( "scripts/config.pl unset $alg" )
+    system( "scripts/config.py unset $alg" )
         and abort "Failed to disable $alg\n";
     for my $opt (@$extras) {
-        system( "scripts/config.pl unset $opt" )
+        system( "scripts/config.py unset $opt" )
             and abort "Failed to disable $opt\n";
     }