It seems that the build 509 is the last build in the current development branch. And I guess it remains to be the only available for the next couple of months.
The new build(s) is currently in beta testing phase and it comes with completely replaced scripting engine and compiler. Though it claims backward compatibility, the compatibility applies only to the pure MQL4 scripts, which were compiled by any of the previous compilers. The new compiler won't compile the recent source files (mq4).
The directory structure changed as well, so indicators and scripts are now merged into a MQL4 folder.
Unfortunately, users of RangeBar, RenkoBar, TickBar and MeanrenkoBar will not be able to use the currently downloaded indicators with the new build. I am preparing a concurrent release for the new MT4 build and I will create a new download area for it, not to mess with the current one.
Update: The current version of the above mentioned indicators is already compatible with the beta release. You may take a test run with the new beta.
For those, who feel comfortably with the PC and want to test the compatibility of their current sets of indicator, there is a guide in the Russian forum, how to get the new beta. In English it is:
Create a new and clean MT4 installation into a new folder (do not even think of updating your current live installation). You may need to Download MetaTrader 4 Terminal Installer (455 Kb)
Try to login, with server field set to demo.metaquotes.net:444 (with no success)
Apply for a new account, with the demo.metaquotes.net:444 server selected.
Shut down the terminal. Reopen this installation of terminal. Update of beta commences and you get the new beta installed.
If you try, try it on your own risk. I disclaim any responsibility.
Nevertheless feel free to discuss it.