imap-send.c: fix compiler warnings for OpenSSL 1.0

The openssl/CHANGES file says:

    Let the TLSv1_method() etc. functions return a 'const' SSL_METHOD
    pointer and make the SSL_METHOD parameter in SSL_CTX_new,
    SSL_CTX_set_ssl_version and SSL_set_ssl_method 'const'.

In older versions, unqualified pointers were used, so we unfortunately
cannot unconditionally update the type of the variable we use.

Signed-off-by: Vietor Liu <vietor@vxwo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

imap-send.c

@@ -272,8 +272,12 @@ static int ssl_socket_connect(struct imap_socket *sock, int use_tls_only, int ve
 #ifdef NO_OPENSSL
 	fprintf(stderr, "SSL requested but SSL support not compiled in\n");
 	return -1;
+#else
+#if (OPENSSL_VERSION_NUMBER >= 0x10000000L)
+	const SSL_METHOD *meth;
 #else
 	SSL_METHOD *meth;
+#endif
 	SSL_CTX *ctx;
 	int ret;