Allow to override UserAgent

Adding on command line the user agent add a duplicate header:

```
./w3m -header "User-Agent: Mozilla" http://localhost:9999

GET / HTTP/1.0
User-Agent: w3m/0.5.3+git20190105
Accept: text/html, text/*;q=0.5, image/*, application/*, message/*, x-scheme-handler/*, audio/*, video/*, inode/*
Accept-Encoding: gzip, compress, bzip, bzip2, deflate
Accept-Language: en;q=1.0
Host: localhost:9999
Pragma: no-cache
Cache-control: no-cache
User-Agent: Mozilla
```

As a result most server will take the first given; the default
w3m_version or the one defined on config `user_agent`

With this patch we can now override `User-Agent` from command line

1 files changed, 8 insertions, 6 deletions

diff --git a/url.c b/url.c
index 1c17e18..31d7c4b 100644
--- a/url.c
+++ b/url.c
@@ -1324,12 +1324,14 @@ otherinfo(ParsedURL *target, ParsedURL *current, char *referer)
     const int *no_referer_ptr;
     int no_referer;
 
-    Strcat_charp(s, "User-Agent: ");
-    if (UserAgent == NULL || *UserAgent == '\0')
-	Strcat_charp(s, w3m_version);
-    else
-	Strcat_charp(s, UserAgent);
-    Strcat_charp(s, "\r\n");
+    if (!override_user_agent) {
+        Strcat_charp(s, "User-Agent: ");
+        if (UserAgent == NULL || *UserAgent == '\0')
+            Strcat_charp(s, w3m_version);
+        else
+            Strcat_charp(s, UserAgent);
+        Strcat_charp(s, "\r\n");
+    }
 
     Strcat_m_charp(s, "Accept: ", AcceptMedia, "\r\n", NULL);
     Strcat_m_charp(s, "Accept-Encoding: ", AcceptEncoding, "\r\n", NULL);