Support dual login via LDAP and forms authentication

Closes #256 as we now support dual login -- LDAP and forms authentication.

Also bumped the vendored library to LDAP.v3 as it contains bug fixes.

vendor/gopkg.in/ldap.v3/client.go

@@ -0,0 +1,28 @@
+package ldap
+
+import (
+	"crypto/tls"
+	"time"
+)
+
+// Client knows how to interact with an LDAP server
+type Client interface {
+	Start()
+	StartTLS(config *tls.Config) error
+	Close()
+	SetTimeout(time.Duration)
+
+	Bind(username, password string) error
+	SimpleBind(simpleBindRequest *SimpleBindRequest) (*SimpleBindResult, error)
+
+	Add(addRequest *AddRequest) error
+	Del(delRequest *DelRequest) error
+	Modify(modifyRequest *ModifyRequest) error
+	ModifyDN(modifyDNRequest *ModifyDNRequest) error
+
+	Compare(dn, attribute, value string) (bool, error)
+	PasswordModify(passwordModifyRequest *PasswordModifyRequest) (*PasswordModifyResult, error)
+
+	Search(searchRequest *SearchRequest) (*SearchResult, error)
+	SearchWithPaging(searchRequest *SearchRequest, pagingSize uint32) (*SearchResult, error)
+}