fix non error assignment to blank
detect unchecked type assertions
unit tests unchecked type assertions

Conflicts:
	lib/errcheck_test.go
Rename -types to -asserts

Conflicts:
	main.go
Go's sub-repositories moved

See
https://groups.google.com/forum/#!topic/golang-nuts/eD8dh3T9yyA/discussion

Conflicts:
	lib/errcheck.go
always use the latest Go version