Avoid a confusing later panic if linting files across packages.

The usage declares that golint only accepts files from a single package,
so now we gracefully enforce that.

Fixes #63.
1 file changed
tree: 725fbe4a5d54369ff56ae11c5c4b0cafa1d552a5
  1. golint/
  2. misc/
  3. testdata/
  4. LICENSE
  5. lint.go
  6. lint_test.go
  7. README