keep in line with MRI if possible

[mkristian]

keep the default x509 certs and directories in line with MRI, only if
they do not exists fallback on cacerts from the java.home/lib/security/cacerts

fixes #49 and keeps the idea of b914091

Sponsored by Lookout Inc.

[mkristian]

@kares @headius please have a look this.

[kares]

makes sense - hopefully there won't be any drawbacks if there are any we can make a system-prop switch

[kares]

on a second note (without looking) will we actually use X509_CERT_AREA if it points to OpenSSL's cert dir since the SSL engine will have those available from Java for sure (as reported in jruby/jruby#1953).

... cert lookup will honor these, although by default does nothing, right?

[mkristian]

X509_CERT_AREA is not used but the X509_CERT_DIR and X509_CERT_FILE

actually b914091 made those two to be used.

still jruby/jruby#1953 says paths are different then on ubuntu. will look into this.

[mkristian]

did not expect to step in such a jungle: https://www.happyassassin.net/2015/01/12/a-note-about-ssltls-trusted-certificate-stores-and-platforms/