Additional functions

[dja852]

Added the following additional functions:

• x509_version: returns x509 version number of certificate
• x509_bcca: checks for Basic Constraints CA extension. Returns TRUE if BC extension present and CA=true, False if BC extension present and CA=false, NULL if Basic Constraints not present
• x509_keyusage: returns integer value of enabled key usage bits
• x509_printkeyusage: returns string text of all enabled key usage bits
• x509_hasExtension_critical: slightly different behaviour than has_extension. This function returns TRUE if extension present AND critical, FALSE if extension present and NOT critical, NULL if extension not present