Critical Preflight Checks

After discussions with Spiderr, we agreed that critical checks will be performed in TikiSystem::checkEnvironment(). Have consolidated methods used to check these settings to ))preflight_inc.php(( and checkEnvironment() will begin to use these functions.

• Reverted changes made to TikiSystem previously (thanks spiderr)
• Added simple preflight checks to ))preflight_inc.php(( such as:
  • minimum PHP version
  • minimum PHP extension version
  • file writeable checks
  • directory writeable checks
  • PHP.ini checks
• In TikiSystem.php
  • moved checkEnvironment() to be one of the first actions during initalisation.
  • moved $checked variable to the end of checkEnvironment() function to ensure all checks are passed.
  • removed directory checks for storage and kernel/config_inc.php from checkEnvironment(), as they are checked again (with a nicer interface) in the installer.
  • Redirect to install/install.php?step=1 if all critical checks pass, but system is not configured.