Intercept SIGINT signal on tests suites

If the function `pcntl_signal()` exists creates an signal handler for SIGINT which prints the summary of test suite and generates code coverage reports.
Move on `PHPUnit_TextUI_TestRunner` all code which prints results and generates coverage from `doRun()` method to `doPrintResult()` method.
Honestly I don't know too much about PHPUnit's core, but I think this is a good feature. If someone could measure the impact of this feature or also give me some tip about how can I create a test for it I will be glad.