This patch fixes typos in xnee_error.c.

There is one more typo I didn't fix because I didn't know what you meant:

    /* XNEE_SCREEN_MISSING */
    "Screen nr could not be retrieved",
    "Xnee could not find the screen of the recorded event. Report the problem",

What did you mean by "nr"? Did you mean "number"? If so, write that. It may not matter; I couldn't find anywhere that `XNEE_SCREEN_MISSING` was used in the code. Maybe this error message can just be removed.

There was also a problem with `XNEE_LAST_ERROR` in that the preceding string had not been terminated with a comma. I don't know what effect fixing this bug will have on your program so you may want to check it.

I didn't fix the typos in the enums (`XNEE_NO_PROT_CHOOSEN` should be `XNEE_NO_PROT_CHOSEN` and `XNEE_AMBIGOUS_CMD` should be `XNEE_AMBIGUOUS_CMD`) since these are in the xnee.h header so they may be part of your public API? Then again the header doesn't get installed. (Should it?)