Allow compiling without go-sql-driver/mysql pkg

This ensures the writefreely pkg can be used in other applications that
need to load mysql themselves -- this can be done by building with the
tag: wflib

Ref T613

app.go

@@ -24,8 +24,6 @@ import (
 	"syscall"
 	"time"
 
-	_ "github.com/go-sql-driver/mysql"
-
 	"github.com/gorilla/mux"
 	"github.com/gorilla/schema"
 	"github.com/gorilla/sessions"

database-lib.go

@@ -0,0 +1,20 @@
+// +build wflib
+
+/*
+ * Copyright © 2019 A Bunch Tell LLC.
+ *
+ * This file is part of WriteFreely.
+ *
+ * WriteFreely is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, included
+ * in the LICENSE file in this source code package.
+ */
+
+// This file contains dummy database funcs for when writefreely is used as a
+// library.
+
+package writefreely
+
+func (db *datastore) isDuplicateKeyErr(err error) bool {
+	return false
+}

database-no-sqlite.go

@@ -1,4 +1,4 @@
-// +build !sqlite
+// +build !sqlite,!wflib
 
 /*
  * Copyright © 2019 A Bunch Tell LLC.

database-sqlite.go

@@ -1,4 +1,4 @@
-// +build sqlite
+// +build sqlite,!wflib
 
 /*
  * Copyright © 2019 A Bunch Tell LLC.