Adding this as an option to avoid breaking people's tests.
Some of the test results show pretty clearly that we are incorrectly
assigning the same comment multiple times for nested nodes (mentioned
in #36).
When parsing on PHP 7 we will no longer be able to deal with
code that contains invalid octal literals. Currently we'll fatal,
after engine exceptions land we'll throw an exception instead.
Travis 5.2 seems to have changed the float output precision, so a test was
failing. Now the numbers in the expected output are also provided by PHP,
so they should be the same.
