Description:
------------
If an arugment is `unset` inside of a function, it is also `unset` from the call stack and corrupts the argument array in the backtrace. This leads to a corrupt array that has a count > 0 and no elements within it. This happens with both debug_backtrace() and getTraceAsString() in the \Exception class.

Test script:
---------------
https://gist.github.com/terpfear/4adab63546659d1f3cab

Expected result:
----------------
Results obtained from php 5.5.9
array(2) {
  [0] =>
  string(6) "string"
  [1] =>
  string(13) "anything else"
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace('string', 'anything else')

unsetting arg1
array(2) {
  [0] =>
  string(6) "string"
  [1] =>
  string(13) "anything else"
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace('string', 'anything else')

unsetting arg2
array(2) {
  [0] =>
  string(6) "string"
  [1] =>
  string(13) "anything else"
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace('string', 'anything else')


Actual result:
--------------
array(2) {
  [0]=>
  string(6) "string"
  [1]=>
  string(13) "anything else"
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace('string', 'anything else')

unsetting arg1
array(2) {
  [1]=>
  string(13) "anything else"
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace('anything else')

unsetting arg2
array(2) {
}
	1) /home/scottf/sandbox/funsies/phpFun/php7BreakingArray.php(18): brokenTrace()