Add default sslproxy configuration (bug #829674)

This was missing and the error logs were being polluted as a result.

Change-Id: I80e6315d25fd1ccb71e37e77f7922784ec3d72ed
Signed-off-by: Melissa Draper <melissa@catalyst.net.nz>

htdocs/lib/config-defaults.php

@@ -237,3 +237,6 @@ $cfg->leapovermnetloglevel = 0;
 // Set a fixed height in pixels for the tinymce editor (currently only
 // affects the textbox blocktype):
 // $cfg->blockeditorheight = 550;
+
+// This needs to be true when forcing https with an ssl proxy such as nginx.
+$cfg->sslproxy = false;