chacha20 comes in two variants: ietf rfc7539, using 96 bit iv and 32 bit counter
and draft-agl-tls-chacha20poly1305 using 64 bit iv and a 64 bit counter. so
setupChachastate() now takes a ivlen argument which sets the mode.
add ccpoly_encrypt()/ccpoly_decrypt() routines.
to implement timing safe ccpoly_decrypt(), a constant time memcmp was needed, so
adding tsmemcmp() to libsec.
