Some changes needed to integrated into the Chromium build system.
Add pyasn1_modules which will replace pyx509.

pyx509 is GPL so not available for use in Chromium Android ASOP.
Adding my own x509 decoder based on pyasn1.

This replaces the GPL pyx509.
Removing pyx509.
Add license text crediting Chromium Authors (ie. I :-) ).