title: How to install golang 3rd-party projects from download sources?
body: <p>I'm trying to install <a href="http://labix.org/mgo">mgo</a> which is a mongo-driver written in golang. </p>
  
  <p>The standard command: </p>
  
  <pre><code>go get launchpad.net/mgo
  </code></pre>
  
  <p>But it failed because of some cert issues.</p>
  
  <p>So I manually download the sources of mgo to local <code>E:\mgo</code>, but I don't know to how install it.</p>
  
  <p>The file tree:</p>
  
  <pre><code>├─.bzr
  │  ├─branch
  │  │  └─lock
  │  ├─branch-lock
  │  ├─checkout
  │  │  └─lock
  │  └─repository
  │      ├─indices
  │      ├─lock
  │      ├─obsolete_packs
  │      ├─packs
  │      └─upload
  ├─bson
  └─testdb
  </code></pre>
  
  <p>I tried:</p>
  
  <pre><code>cd mgo
  go install
  </code></pre>
  
  <p>It reports:</p>
  
  <pre><code>auth.go:34:2: import "launchpad.net/mgo/bson": cannot find package
  </code></pre>
  
  <p>But if I try to install bson first:</p>
  
  <pre><code>cd bson
  go install
  </code></pre>
  
  <p>It reports another error:</p>
  
  <pre><code>go install: no install location for _/E_/mgo/bson
  </code></pre>
  
  <p>So, what's the correct command to install it?</p>