conflict in travis php versions and applied unit tests

[goatherd]

as support for multiple PHP versions was added unit tests will fail if the test assumption is not matched.

In especially PHP 5.3 env will not report function names deprecated since 5.5 by default.

[goatherd]

@reneoelke @Ephigenia there are two options to fix this:

• do only test compatibility up to the current PHP version
• do always test anything and skip unsupported features (like trait keyword)

What would you expect a PHP 5.3 user to test against by default?
PHP 5.3 compat or newest PHP compat?
Is this the same setting we want to be covered by unit tests for that version?

It is still possible to set compat version range by cli argument.

[goatherd]

@reneoelke according to our talk the test will get simplified and we concentrate on 5.5 support for now.

The functionality part is answered by #15. The remainder we may discuss later on.