CHOP-956: Add settings_install.xml to settings_files.xml.

Also clarify comment for ELLPath in lldir.h: ELLPath int values are read from
settings_files.xml.

indra/llvfs/lldir.h

@@ -32,7 +32,7 @@
 #define MAX_PATH MAXPATHLEN
 #endif
 
-// these numbers *may* get serialized (really??), so we need to be explicit
+// these numbers are read from settings_files.xml, so we need to be explicit
 typedef enum ELLPath
 {
 	LL_PATH_NONE = 0,

indra/newview/app_settings/settings_files.xml

@@ -4,6 +4,9 @@
     <file name="Global"
           file_name="settings.xml"
           required="true"/>
+    <file name="Global"
+          file_name="settings_install.xml"
+          required="false"/>
     <file name="PerAccount"
           file_name="settings_per_account.xml"
           required="true"/>