Export X509_STORE_load_locations and X509_STORE_set_default_paths 

Hi. I faced with necessity to verify certificates offline and found that some OpenSSL functions required for this task are missed. OpenSSL provides X509_STORE_CTX for certificate verification, X509_STORE_CTX uses X509_STORE as input, but some functions that allow to configure store are missed. This pull request adds 2 functions X509_STORE_load_locations and X509_STORE_set_default_paths that can be used to configure X509_STORE.