Error during install: An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows.

@andygraybeal reported this issue in IRC #farmOS, and shared login info with me so that I could help debug.

Symptoms:

• Error during installation: An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /install.php?profile=farm&locale=en&id=1&op=do StatusText: Internal Server Error ResponseText:
• PHP notice throughout: Notice: Undefined index: distribution_name in drupal_install_profile_distribution_name() (line 207 of /includes/install.inc).
• Only Farm Area and Farm Map modules install. If you try to install any of the others, WSOD (white screen of death). We weren't able to find any helpful messages in dblog or Apache logs.

I think I fixed the second one (Undefined index: distribution_name) by adding a distribution_name line to farm.info (see recent commit).