Handle Visual C warning about non-standard function names.

Visual C version from version 2003 complain about certain function
names, for example:

    apps\apps.c(2572) : warning C4996: 'open': The POSIX name for this item is deprecated. Instead, use the ISO C++ conformant name: _open. See online help for details.

This adds preprocessor aliases for them in e_os.h.

Additionally, crypto/conf/conf_lib.c needs to include e_os.h to catch
those aliases.

RT#4488
RT#4489

Reviewed-by: Matt Caswell <matt@openssl.org>