action attribute of form is not rewrited by base_url

[GoogleCodeExporter]

**What steps will reproduce the problem?
1. in nginx settings of 1st-domain server, set proxy to 2nd domain
2. in setting.php of neologism on 2nd domain, set
 $base_url='http://2nd-domain/new-path',
 $cookie_domain='2nd-domain',
 'reverse_proxy' => TRUE, 
 'reverse_proxy_addresses' => array('1st-domain-ip')
3. install
4. vocabulary import form and login form (maybe and any other submit form) are 
broken.
 In other words, action attribute of form is not rewrited by $base_url.

**What is the expected output? 
By pushing 'Log in' button, Log in.

**What do you see instead?
Redirected to "http://2nd-domain/old-path//user" and 404 come back.

**What version of the product are you using? On what operating system?
Neologism 0.5.3
Ubuntu 12.04

**Please provide any additional information below.
By executing,
javascript:document.forms[0].action = location.href
this problem can be temporarily solved. 

Original issue reported on code.google.com by Akihiro....@gmail.com on 19 Jul 2013 at 10:49