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.
This is step 1 of a plan to get rid once and for all of missing depends_on in
the X509 test suite (step 2 will be RSA/ECDSA, and step 0 was curves.pl).