Could you please explain the meaning of code in "Pre-compiling binaries" section of README.md file?
It looks like initial environment initialization, but I'm not sure it's executed properly.
There's lines related to installation of PEAR and, then, APC, but I can't find APC in the list of installed PHP extensions.
Yes, APC was broken initially. The current version installed now has APC enabled on Heroku. Due to limitations of our buildpack system, if you have any existing PHP apps you have it enabled on, you'll need to re-push your app. Just create some trivial git commit (like, adding a newline or comment somewhere) and do a git push to heroku. That'll repackage your slug and pull in the version with APC enabled. If you do that, you should also be get PHP 5.3.10 pulled in. If APC still isn't working, please let me know.
The "pre-compiling binaries" is documentation for maintainers of the buildpack, or anyone who wants to fork the buildpack. People writing PHP apps shouldn't need to concern themselves with it too much. Currently, at Heroku we're handling that compilation in an excessively manual way. That binary compilation part needs to refactored at some point in the future to be built via Vulcan (https://github.com/heroku/vulcan), so it's a little easier to deal with. The directions will be radically changed then.
Enable mod_deflate in httpd.conf #2
Possible change #2.