fixed #50: run APC(u) tests in travis

[marc-mabe]

This (re)-enables APC adapter tests on travis (#50)

• using apcu-4.0.8 (currently last stable) extension on PHP < 7
• using apcu_bc (last beta) extension on PHP 7
  • There is a bug using pecl install apcu_bc-beta where it attaches the directive extension=apc.so on top of php.ini which results in wrong extension loading :(
  • To solve that issue I added another ini file loading the extension in bottom which still results in a warning of the first load but the test works
    -> @Maks3w other ideas ?

[Maks3w]

ok for me. Workaround is enough documented.