Remove trailing null byte from X509_Time::to_string

Make invalid tag case report the value
Have OCSP responses return an enum allowing a range of conditions to be expressed
(good status, cert revoked, some other error, etc).

Add a certificate store backed by files (requiring boost filesystem).

Change Certificate_Store interface somewhat to support retrieval without copying.
Split chain creation and checking
Move OCSP to x509 subdir as they are quite entangled
Disable RC4 in TLS by default
Remove timeout from HTTP
First pass at automatic OCSP checks