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/curves.pl b/tests/scripts/curves.pl
index 4791d55..3e22552 100755
--- a/tests/scripts/curves.pl
+++ b/tests/scripts/curves.pl
@@ -46,13 +46,13 @@
     system( "make clean" ) and die;
 
     # depends on a specific curve. Also, ignore error if it wasn't enabled
-    system( "scripts/config.pl unset MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED" );
+    system( "scripts/config.py unset MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED" );
 
     print "\n******************************************\n";
     print "* Testing without curve: $curve\n";
     print "******************************************\n";
 
-    system( "scripts/config.pl unset $curve" )
+    system( "scripts/config.py unset $curve" )
         and abort "Failed to disable $curve\n";
 
     system( "CFLAGS='-Werror -Wall -Wextra' make lib" )