Resolve linter errors exposed by fixed Makefile

- TravisCI didn't like "POSIX" ::= syntax

pkg/storage/file/fmessage.go

@@ -11,8 +11,8 @@ import (
 	"time"
 
 	"github.com/jhillyerd/enmime"
-	"github.com/jhillyerd/inbucket/pkg/storage"
 	"github.com/jhillyerd/inbucket/pkg/log"
+	"github.com/jhillyerd/inbucket/pkg/storage"
 )
 
 // FileMessage implements Message and contains a little bit of data about a

pkg/storage/file/fstore.go

@@ -12,8 +12,8 @@ import (
 	"time"
 
 	"github.com/jhillyerd/inbucket/pkg/config"
-	"github.com/jhillyerd/inbucket/pkg/storage"
 	"github.com/jhillyerd/inbucket/pkg/log"
+	"github.com/jhillyerd/inbucket/pkg/storage"
 	"github.com/jhillyerd/inbucket/pkg/stringutil"
 )
 
@@ -140,6 +140,7 @@ func (ds *FileDataStore) AllMailboxes() ([]datastore.Mailbox, error) {
 	return mailboxes, nil
 }
 
+// LockFor returns the RWMutex for this mailbox, or an error.
 func (ds *FileDataStore) LockFor(emailAddress string) (*sync.RWMutex, error) {
 	name, err := stringutil.ParseMailboxName(emailAddress)
 	if err != nil {

pkg/storage/lock.go

@@ -5,8 +5,12 @@ import (
 	"sync"
 )
 
+// HashLock holds a fixed length array of mutexes.  This approach allows concurrent mailbox
+// access in most cases without requiring an infinite number of mutexes.
 type HashLock [4096]sync.RWMutex
 
+// Get returns a RWMutex based on the first 12 bits of the mailbox hash.  Hash must be a hexidecimal
+// string of three or more characters.
 func (h *HashLock) Get(hash string) *sync.RWMutex {
 	if len(hash) < 3 {
 		return nil

pkg/storage/testing.go

@@ -27,6 +27,7 @@ func (m *MockDataStore) AllMailboxes() ([]Mailbox, error) {
 	return args.Get(0).([]Mailbox), args.Error(1)
 }
 
+// LockFor mock function returns a new RWMutex, never errors.
 func (m *MockDataStore) LockFor(name string) (*sync.RWMutex, error) {
 	return &sync.RWMutex{}, nil
 }