add T_POW (**) operator

Fixed recognition of the operator

Added opcode, still doing multiply instead of pow()

opcode now always returns int(42)

The right answer, but always a float

Yanked code from pow() implementation.

Should not handle negative long as exponent ourselves

Added test cases from pow()

Moved precedence higher than '~'

Added GMP operator overloading

Added ZEND_ASSIGN_POW (**=) operator.

Added pow() as a language construct.

Adjusted test cases for changed precedence.

Reduced pow() to shell function around ZEND_API pow_function()

Reduced test case to only contain edge cases
Added overloading test case

Moved unary minus above T_POW

Revert "Added pow() as a language construct."

Bad bad bad idea.

This reverts commit f60b98cf7a8371233d800a6faa286ddba4432d02.

Reverted unary minus behaviour due to previous revert.
Convert arrays to int(0)
Exponent with array as a base becomes int(0)

Rebase against master

Fixed tokenizer test case
Added information in NEWS and UPGRADING