Put error output from M-! at the end of the error buffer

* lisp/simple.el (shell-command-on-region): Put the error output
at the end of the buffer instead of wherever point is (bug#7513).
This avoids interleaving error output.
1 job for master in 7 minutes and 53 seconds (queued for 5 seconds)
Status Job ID Name Coverage
failed #3098


Name Stage Failure
test-all Test
Makefile:402: recipe for target 'xdisp.o' failed
make[2]: Leaving directory '/builds/emacs/emacs/src'
make[2]: *** [xdisp.o] Error 1
Makefile:424: recipe for target 'src' failed
make[1]: *** [src] Error 2
make[1]: Leaving directory '/builds/emacs/emacs'
Makefile:1117: recipe for target 'bootstrap' failed
make: *** [bootstrap] Error 2
ERROR: Job failed: exit code 1