Port Viewer 2 indra/llvfs

This introduces some API changes, like the new LLDirIterator,
that causes changes elsewhere.

It also include Log Linden's cache changes that aren't in
viewer-development yet that increase the maximum cache size
to ~10 GB.

indra/newview/app_settings/settings.xml

@@ -4623,6 +4623,17 @@
       <key>Value</key>
       <integer>4</integer>
     </map>
+    <key>DumpVFSCaches</key>
+    <map>
+      <key>Comment</key>
+      <string>Dump VFS caches on startup.</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>Boolean</string>
+      <key>Value</key>
+      <integer>0</integer>
+    </map>
     <key>DynamicCameraStrength</key>
     <map>
       <key>Comment</key>