Merge branch 'coalesce_operator'

* coalesce_operator:
  Extended coalesce operator test case for ordering/short-circuiting
  Ensure not evaluated twice
  Added test
  Initial coalesce operator implementation

diff --cc Zend/zend_ast.h
Simple merge

diff --cc Zend/zend_compile.c
Simple merge

diff --cc Zend/zend_opcode.c
Simple merge

diff --cc Zend/zend_vm_def.h
Simple merge

diff --cc Zend/zend_vm_execute.h
Simple merge

diff --cc Zend/zend_vm_opcodes.c
Simple merge

diff --cc Zend/zend_vm_opcodes.h
Simple merge