Allow specifying an export macro
Remove unused variable

The variable hasn't been used since 2a4f9b7. Throws a warning when
building ZNC:

Csocket.h:1115:34: warning:
private field 'm_bBLOCK' is not used [-Wunused-private-field]
Fix const correctness

NOTE: the signature of the following virtual methods has changed:
- GetPending()
- ConvertAddress()
Support ECDHE exchange if available in OpenSSL
prefer tab spacing, tabstop=4 in vim
add openssl's fix for POODLE bug in server mode. Give Csocket consumers the ability to disable less desirable protocols