Fix rune count in X, x event messages

[paul-lalonde]

After careful review of the original acme code and of Russ's go port, yes, "character count" in the man page is number of runes, not bytes. This fixes the two mis-matched occurences I could see.

[codecov[bot]]

Codecov Report

Merging #490 (96c093b) into master (73ec48e) will increase coverage by 0.01%. The diff coverage is 0.00%.

:exclamation: Current head 96c093b differs from pull request most recent head 8cd9f5e. Consider uploading reports for the commit 8cd9f5e to get more accurate results

@@            Coverage Diff             @@
##           master     #490      +/-   ##
==========================================
+ Coverage   58.47%   58.48%   +0.01%     
==========================================
  Files          54       54              
  Lines       10761    10761              
==========================================
+ Hits         6292     6294       +2     
+ Misses       4033     4032       -1     
+ Partials      436      435       -1     

Impacted Files	Coverage Δ
exec.go	38.06% <0.00%> (ø)

... and 1 file with indirect coverage changes