Refer to OPENSSLDIR rather than "the OpenSSL install directory"

The prior wording was less accurate.
See https://github.com/openssl/openssl/pull/1372#discussion_r73127000.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>

doc/crypto/CTLOG_STORE_new.pod

@@ -25,8 +25,8 @@ logs). The list can be loaded from one or more files and then searched by LogID
 CTLOG_STORE_new() creates an empty list of CT logs. This is then populated
 by CTLOG_STORE_load_default_file() or CTLOG_STORE_load_file().
 CTLOG_STORE_load_default_file() loads from the default file, which is named
-"ct_log_list.cnf" in the OpenSSL install directory. This can be overridden using
-an environment variable named "CTLOG_FILE".
+"ct_log_list.cnf" in OPENSSLDIR (see the output of L<version>). This can be
+overridden using an environment variable named "CTLOG_FILE".
 CTLOG_STORE_load_file() loads from a caller-specified file path instead.
 Both of these functions append any loaded CT logs to the CTLOG_STORE.