MINOR: ssl: add debug traces

MINOR: ssl: add debug traces

Add some debug trace when haproxy is configured in debug & verbose mode.
This is useful for openssl tests. Typically, the error "SSL handshake
failure" can be caused by a lot of protocol error. This patch details
the encountered error. For exemple:

   OpenSSL error 0x1408a0c1: ssl3_get_client_hello: no shared cipher

Note that my compilator (gcc-4.7) refuse to considers the function
ssl_sock_dump_errors() as inline. The condition "if" ensure that the
content of the function is not executed in normal case. It should be
a pity to call a function just for testing its execution condition, so
I use the macro "forceinline".