[Fix #476] Disable syntax checkers that report excessive errors
Never allow use of disabled checkers
Merge branch 'disable-excessive-checkers'

* disable-excessive-checkers:
  Never allow use of disabled checkers
  [Fix #476] Disable syntax checkers that report excessive errors
Update documentation
Update texinfo manual
Simplify error region functions
Don't chase symlinks in -same-files-p
Merge branch 'speedup'

* speedup:
  Don't chase symlinks in -same-files-p
  Simplify error region functions
Update changelog

[ci skip]