Properly handle user-switching in adduser

Re: npm/npm-registry-couchapp#73

lib/adduser.js

@@ -39,7 +39,20 @@ function adduser (username, password, email, cb) {
       , date: new Date().toISOString()
       }
 
-  cb = done.call(this, cb)
+  // pluck off any other username/password/token.  it needs to be the
+  // same as the user we're becoming now.  replace them on error.
+  var pre = { username: this.username
+            , password: this.password
+            , auth: this.auth
+            , token: this.token }
+
+  this.token = null
+  this.couchLogin.token = null
+  this.username = username
+  this.password = password
+  this.auth = new Buffer(username + ':' + password).toString('base64')
+
+  cb = done.call(this, cb, pre)
 
   var logObj = Object.keys(userobj).map(function (k) {
     if (k === 'salt' || k === 'password_sha') return [k, 'XXXXX']
@@ -50,6 +63,7 @@ function adduser (username, password, email, cb) {
   }, {})
 
   this.log.verbose("adduser", "before first PUT", logObj)
+
   this.request('PUT'
     , '/-/user/org.couchdb.user:'+encodeURIComponent(username)
     , userobj
@@ -89,11 +103,21 @@ function adduser (username, password, email, cb) {
       }.bind(this))
 }
 
-function done (cb) {
+function done (cb, pre) {
   return function (error, data, json, response) {
     if (!error && (!response || response.statusCode === 201)) {
       return cb(error, data, json, response)
     }
+
+    // there was some kind of error, re-instate previous auth/token/etc.
+    this.couchLogin.token = this.token = pre.token
+    if (this.couchLogin.tokenSet) {
+      this.couchLogin.tokenSet(pre.token)
+    }
+    this.username = pre.username
+    this.password = pre.password
+    this.auth = pre.auth
+
     this.log.verbose("adduser", "back", [error, data, json])
     if (!error) {
       error = new Error( (response && response.statusCode || "") + " "+