Lint everything

We were ignoring quite a few error cases, and had one case where we weren't
actually updating state where we wanted to. Unfortunately, if the linter doesn't
pass, nobody has any reason to actually check lint failures in CI.

There are three remaining XXXs marked in the code for lint.

node/impl/client/client.go

@@ -109,7 +109,7 @@ func (a *API) ClientStartDeal(ctx context.Context, params *api.StartDealParams)
 				continue
 			}
 			if c.Equals(params.Data.Root) {
-				storeID = &importID
+				storeID = &importID //nolint
 				break
 			}
 		}
@@ -614,7 +614,7 @@ func (a *API) ClientCalcCommP(ctx context.Context, inpath string) (*api.CommPRet
 	if err != nil {
 		return nil, err
 	}
-	defer rdr.Close()
+	defer rdr.Close() //nolint:errcheck
 
 	stat, err := rdr.Stat()
 	if err != nil {
@@ -700,7 +700,7 @@ func (a *API) clientImport(ctx context.Context, ref api.FileRef, store *multisto
 	if err != nil {
 		return cid.Undef, err
 	}
-	defer f.Close()
+	defer f.Close() //nolint:errcheck
 
 	stat, err := f.Stat()
 	if err != nil {