Composer >1.3.0 compatibility

[barchard]

Composer 1.3.0 now reloads PHP in order to disable XDebug. This results in the following error being generated whenever the library is used:

PHP Warning:  Module 'pcntl' already loaded in Unknown on line 0

Warning: Module 'pcntl' already loaded in Unknown on line 0

other packages are affected by this too. more info:

https://github.com/Homebrew/homebrew-php/issues/3896#issuecomment-271522581
https://github.com/sensiolabs/SensioDistributionBundle/pull/304/files