LP#1343578: Add support for log tagging

The ability to provide instance-specific log tagging via syslog
would make running multiple instances much easier to manage.  So
this branch does that.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
LP#1343578: Perl/C syslog "logtag" additions.

 * Honor logtag value when applying a default appname for Perl and C
 * Extract / apply logtag in the router
 * Minor repair: avoid redundant strdup

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
LP#1343578: document <logtag> in the example opensrf_core.xml

Signed-off-by: Galen Charlton <gmc@esilibrary.com>