all: use charm.v4

Automatic change made by running:

	govers gopkg.in/charm.v4
	govers -m launchpad.net/gocheck gopkg.in/check.v1
Merge pull request #116 from rogpeppe/052-use-charm.v4

all: use charm.v4

Automatic change made by running:

	govers gopkg.in/charm.v4
	govers -m launchpad.net/gocheck gopkg.in/check.v1