avoid overwriting include path

[glensc]

• fixes pear bug http://pear.php.net/bugs/bug.php?id=17045
• refs e115fc9, de36f63, 51c697a, 9c19304
• solves installation via composer where other pear packaegs are NOT
  installed to same include path as PEAR package itself

[glensc]

If interested testing of the failure with composer, create composer.json:

{
    "repositories": [
        {
            "type": "pear",
            "url": "http://pear.php.net",
            "vendor-alias": "pear"
        }
    ],
    "require": {
        "pear-pear.php.net/PEAR": "*"
    }
}

and run:

 composer.phar install
 vendor/bin/pear

Warning: require_once(Console/Getopt.php): failed to open stream: No such file or directory in System.php on line 21

Warning: require_once(Console/Getopt.php): failed to open stream: No such file or directory in /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/System.php on line 21

Call Stack:
    0.0012     900320   1. {main}() /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/pearcmd.php:0
    0.0069    2010600   2. require_once('/Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/PEAR/Config.php') /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/pearcmd.php:52
    0.0153    3856128   3. require_once('/Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/System.php') /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/PEAR/Config.php:24


Fatal error: require_once(): Failed opening required 'Console/Getopt.php' (include_path='/Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR') in /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/System.php on line 21

Call Stack:
    0.0012     900320   1. {main}() /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/pearcmd.php:0
    0.0069    2010600   2. require_once('/Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/PEAR/Config.php') /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/pearcmd.php:52
    0.0153    3856128   3. require_once('/Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/System.php') /Users/glen/scm/bug-17045/vendor/pear-pear.php.net/PEAR/PEAR/Config.php:24