(I25) Fix Xproto deprecation warnings

I made the ```enterLeave::ELFlagFocus``` and ```enterLeave::ELFlagSameScreen``` fields in ```__gshared``` const int because I think it's the closest to a C representation of the struct. 
This is the wrong fix.

The original C code is:
```
#define ELFlagFocus        (1<<0)
#define ELFlagSameScreen   (1<<1)
```

The correct D2 translation would be to use an `enum`.

This fix instead introduces constant struct *fields* with a default value, thus changing the struct's size.