afford more logging (following defaults on Ubuntu);

--- a/src/Pure/Tools/phabricator.scala	Tue Feb 11 17:03:14 2020 +0100
+++ b/src/Pure/Tools/phabricator.scala	Wed Feb 12 16:30:23 2020 +0100
@@ -461,6 +461,8 @@
     DocumentRoot """ + config.home.implode + """/webroot
 
     ErrorLog ${APACHE_LOG_DIR}/error.log
+    CustomLog ${APACHE_LOG_DIR}/access.log combined
+
     RewriteEngine on
     RewriteRule ^(.*)$  /index.php?__path__=$1  [B,L,QSA]
 </VirtualHost>