title: Upgrade git to 1.8.1.5 failed
body: <p>On Ubuntu 10.04.4 LTS, I have upgraded git to 1.8.1.1 using apt-get install<br/>
  Now I downloaded git-1.8.1.5.tar.gz,and want to build the source to upgrade git.<br/>
  I have set the $PATH environment variable in .bashrc <br/></p>
  
  <pre><code>export PATH=/usr/local:$PATH
  </code></pre>
  
  <p>I source .bashrc,and echo $PATH shows the set path '/usr/local:/'<br/>
  When I <br/></p>
  
  <pre><code>make prefix=/usr/local all doc info
  </code></pre>
  
  <p>error comes:<br/></p>
  
  <pre><code>In file included from http.c:1:
  http.h:6:23: warning: curl/curl.h: no such file or directory
  http.h:7:23: warning: curl/easy.h: no such file or directory
  In file included from http.c:1:
  http.h:46: error: expected specifier-qualifier-list before ‘CURLcode’
  http.h:51: error: expected specifier-qualifier-list before ‘CURL’
  http.h:97: error: ‘CURL_ERROR_SIZE’ undeclared here (not in a function)
  http.h: In function ‘missing__target’:
  http.h:102: error: ‘CURLE_FILE_COULDNT_READ_FILE’ undeclared (first use in this function)
  http.h:102: error: (Each undeclared identifier is reported only once
  http.h:102: error: for each function it appears in.)
  http.h:104: error: ‘CURLE_HTTP_NOT_FOUND’ undeclared (first use in this function)
  </code></pre>
  
  <p>anyone can help me find the answer?</p>