>
> I sent a fix, please test [1].
>
> BTW, while investigating it, I found that we will have more
> compatibility issues in the future. It seems that gnutls doesn't
> consider backward compatibility seriously [2].

Your patch compiles fine, but triggers warnings:

schannel_gnutls.c: In function ‘schannel_get_cipher_algid’:
schannel_gnutls.c:275:5: warning: case value ‘93’ not in enumerated type ‘gnutls_cipher_algorithm_t’ [-Wswitch]
     case GNUTLS_CIPHER_AES_128_GCM: return CALG_AES_128;
     ^
schannel_gnutls.c:277:5: warning: case value ‘94’ not in enumerated type ‘gnutls_cipher_algorithm_t’ [-Wswitch]
     case GNUTLS_CIPHER_AES_256_GCM:

I'm on Linux Mint 17. It uses a Trusty base. libgnutls-dev version is 2.12.23 (-12ubuntu2.2)