7.1: to_char(): Y,YY,YYY,YYYY fix

 Hi,

  here is a patch for formatting.c (to_char/timestampt()), for 7.1
 it fixing Y,YY,YYY,YYYY conversion, the docs and regress tests update
 are included too.

  During the patch testing I found small bug in miscadmin.h in
convertstr() declaration. Here it's fixed too.

 Thanks

    Karel


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