node.js previously only used a hard-coded list of CA certificates defined in
src/node_root_certs.h.  This made it difficult for system
administrators to update the CA list or add/remove CAs, as the CA list
both required a recompile of node.js to make changes and required
managing the node.js CA list independently from the CA list used by
other OpenSSL applications on the system.

With this change, node.js will instead use the OpenSSL default CA list
(whose path is defined at OpenSSL compile-time but may be overridden
using the SSL_CERT_FILE or SSL_CERT_DIR environment variables), which
allows node.js to use the same system-wide CA list as other
OpenSSL-based programs, and allows system administrators to easily
update or customize the CA list in a central location without the need
to recompile node.js.  The hard-coded CA list is retained, but is only
used if the OpenSSL default CA list is not available.

node.js currently accepts a 'ca' option to override the default trusted
CA list, however trusted CAs must be manually loaded into a javascript
array by the caller to use this option.

This change adds additional 'caFile' and 'caPath' options which allow
callers to specify the path to a file or path containing trusted CA
certificates.  This allows the trusted CA list to be overridden in the
same manner as is allowed by other OpenSSL-based applications.