Sort files in the default impl of project-files alphabetically

* lisp/progmodes/project.el (project--files-in-directory):
Sort the files alphabetically
(https://debbugs.gnu.org/cgi/bugreport.cgi?bug=23179#296).
1 job for master in 52 minutes and 13 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #1359
test-all

00:52:13

 
Name Stage Failure
failed
test-all Test
Makefile:313: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:288: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1