Fixed test cases

It looks like the test files were using wrong path values. I tried fixing it by prefixing dirname(__FILE__) whereever necessary. While most tests are completing successfully now I'm still having issues with a missing class `Misc` in some cases. For instance:
```
user@ubuntu:~/projects/phpixie$ phpunit tests/system/requestTest.php 
PHPUnit 3.7.18 by Sebastian Bergmann.

PHP Fatal error:  Class 'Misc' not found in /home/user/projects/phpixie/system/classes/request.php on line 72
```