Add support for variadic parameters (PHP 5.6)
Add support for argument unpacking (PHP 5.6)
Add support for pow operator (PHP 5.6)
Add support for constant scalar expressions (PHP 5.6)
Add support for function and constant import (PHP 5.6)
Support use function/const in name resolver
Fix ** emulation wrt comments
Minor cleanups to emulative lexer

Be consistent about version numbers. We'll only emulate until
beta1 of a release, as that's the feature freeze release.
merged nikic branch