The readline module is part of the standard Python package found in most common Linux distributions (Debian/Ubuntu/Mint/Fedora/etc.). The only major Posix distribution requiring an explicit readline installation is Mac OS X. Another notable exception is the ActivePython distribution which also ships without readline.
Mac OS X's default PHP install does not include pcntl. Let's make this optional, so people don't have to recompile PHP just to use phpsh. This commit lets us use the benefits of pcntl if we have it, but doesn't force us to have it.