Avoid a potential null value.

If `$option->type` is neither set to `enable` or `disable`, we will have
a null value for `$t`. Also, I have renamed some variables for a better
readability.
Write the cleanup() method.
Change the visiblity of the _runCommand() method.
Avoid a call to an undefined method.

Throw an exception instead.
Fix PECL package pattern (Closes #25)
Merge pull request #42 from Hywan/runCommand

Update the _runCommand
Merge pull request #43 from Hywan/cleanup

Write the cleanup() method.
Merge pull request #41 from Hywan/configure

Avoid a potential null value