For all users that are previewing Magento via SVN checkout:
With the latest version 0.7.14800 PEAR packages were introduced, allowing users to install and upgrade packages through the administrative interface.
Please note, that currently it is not supported to install PEAR packages over SVN checkout copy, and may cause conflicts between SVN and PEAR files.
If you wish to install version 0.7.14800 using the bootstrap package and have an ability to install and upgrade extensions using Magento Connect PEAR channel, you should install it in a separate folder.
Let me know if you have any questions!
Bye for now