[Fix #461] Drop Projectile integration

Gets in the way of ancestor-based config file locating
Skip test if required modes are missing
Remove last traces of s.el in the test suite

Regression from fca2c54
Add a Coq syntax checker
Provision Coq on test systems
Merge branch 'coq'

* coq:
  Provision Coq on test systems
  Add a Coq syntax checker
  Skip test if required modes are missing

Conflicts:
	test/flycheck-test.el
Update changelog and texinfo manual
First try att dscanner
Use both --syntaxCheck and --styleCheck instead of -s
Remove --styleCheck. Both arguments are not supported.
Add d-dscanner-syntax and d-dscanner-style
Add d-dscanner-style to flycheck-checkers
Defined :next-checkers to d-dmd
Add URL ref for DScanner checkers
Correct use of :next-checkers for D checkers
Always use d-dscanner-style after d-dscanner-syntax because dscanner --syntaxCheck may give false positives
Call d-dscanner-syntax also when d-dmd emits warnings
Use both d-dscanner-syntax and d-dscanner-syntax as :next-checkers for d-dmd