Handle abnormal exit of s_client/s_server processes.

Fixes partially #230.

Support of pkeyutl -pkeyopt ukmhex:0102030405060708 syntax

There need to be more tests than 2 constant fixed size blocks.
Final digest values are generated from the first run.

Test description in comments.

Plus some minor chnages
- function defenition doen't match function declaration
- Consecutive break statement is unnecessary.
- Type missmatch in format string

Only stack buffers are considered.

`RAND_priv_bytes' is supposed to be used for private data.

OpenSSL suggests to use (and internally itself uses)
`BN_{CTX_,}secure_new' primitives to work with private keys.

These are using `OPENSSL_secure_malloc' et al. calls, which use
special 'secure heap' memory.

Along, optimize out `hashsum2bn' with `BN_lebin2bn'.

`Test2::V0' is non standard and rarely present on systems, making `make
test' unnecessarily fail.