PHP cookbook: use APC package from pear instead of distro repo

- Because distro-provided APC package sometimes causes PHP to hang
- Use platform_family instead of node['platform']
- Raise NotImplementedError if platform is not supported
Merge pull request #179 from phunehehe/php-use-latest-apc

PHP cookbook: use APC package from pear instead of distro repo
change variable name to be consistent
add an attribute for wal_keep_segments
default value of archive_timeout is actually 0