Add PHPUnit and PEAR_Log as development requirement.

This way you can run tests without manually installing PEAR packages or PHPUNit itself. After cloning the repository you can run tests with:

%composer install
%vendor/bin/phpunit -c phpunit.xml test/
No need to add /lib/adapters/ to include path.
Merge pull request #362 from tuupola/add-phpunit

Add PHPUnit and PEAR_Log as development requirement.