I only saw this thread after I tried (unsuccessfully) to install 1.6.4. (OS is Win7/64-bit)
I have uninstalled 1.6.4 and deleted the .../AppData/Roaming/Arduino15 folder.
Then, I re-installed 1.6.3 and it all seems to go well until I try to add the RFduino.
When I try to get the RFduino library installed via Tools/Boards Manager, I get the attached message indicating that the ContributedPackage has encounted an unexpected end-of-input.
After this, I can no longer launch Arduino. I get the splash screen, and then nothing until/unless I delete the .../AppData/Roaming/Arduino15 folder again.
Deleting the Arduino15 folder, and removing the rfduino.com server in the Preferences Proxy Settings results in the Boards Manager successfully finding and downloading a couple of Intel boards, but it all goes south as soon as I enter the rfduino.com proxy server.
Any suggestions would be appreciated. Thanks in advance.