Remove superfluous Z_REFCOUNTED_P check

The string is never interned and IS_CONSTANT_EX is always refcounted.
Remove SMART_STR_USE_REALLOC
Use inline functions for most of smart_str

smart_str_free_ex no longer exists, always use smart_str_free instead.

smart_str_alloc no longer requires a newlen variable to be in scope,
instead it returns the new length.
Use append_unsigned instead of append_long where appropriate
Make number printing functions less generic

Now that zend_ulong is 64bit on 64bit platforms, it should be
sufficient to always use it, rather than supporting multiple
types.

API changes:
 * _zend_print_unsigned_to_buf and _zend_print_signed_to_buf
   no longer exist.
 * smart_str(ing)_print_long and smart_str(ing)_print_unsigned
   no longer exist.
 * Instead of all these, zend_print_ulong_to_buf and
   zend_print_long_to_buf should be used.
 * smart_str_append_generic_ex no longer exists.
 * smart_str(ing)_append_off_t(_ex) no longer exists, use
   smart_str(ing)_append_long(_ex) instead.
Make header C++ compatible