+ T_POW implementation (from php 5.6-beta2)
* fixed int if possible for pow result
* fixed pow() behaviour
* fixed long overflow for pow operation
+ tests
Merge branch 'pow-impl' of https://github.com/POPSuL/jphp into POPSuL-pow-impl

Conflicts:
	jphp-core/src/org/develnext/jphp/core/tokenizer/TokenType.java
Merge branch 'POPSuL-pow-impl'