[Fix #465] Don't use null-device for Go

Go still can't write to /dev/null, apparently because it's “too magic”
for the Google engineers.  Who gives a fuck about established Unix
practices?

See https://code.google.com/p/go/issues/detail?id=4851 for details.

Partially reverts 3282449.
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
Remove use of d-dscanner-syntax for now