Add Linux client supporting libcurl4

The updated package bases on 'libcurl4_1202_hotfix' branch, client binary
is new, but server binary isn't changed (it's taken from original release).
The updated package is available at the default link, and the name of
original package is changed to AssaultCube_v1.2.0.2_libcurl3.tar.bz2 .

Author: aurhat

htdocs/SSI-HTML/download_box.html

@@ -14,7 +14,7 @@ <h3>Download it here:</h3>
           </tr>
           <tr>
             <td>
-              <a href="https://github.com/assaultcube/AC/releases/download/v1.2.0.2/AssaultCube_v1.2.0.2.dmg">
+              <a href="../download.html">
               <img src="docs/images/apple.png" alt="Mac OS" width="40px" height="40px" title="Supports Mac OS X 10.6 (or higher)"></a>
             </td>
             <td>
@@ -24,11 +24,11 @@ <h3>Download it here:</h3>
           </tr>
           <tr>
             <td>
-              <a href="https://github.com/assaultcube/AC/releases/download/v1.2.0.2/AssaultCube_v1.2.0.2.tar.bz2">
+              <a href="../download.html">
               <img src="docs/images/linux.png" alt="Linux" width="40px" height="40px" title="Linux"></a>
             </td>
             <td>
-              <a href="https://github.com/assaultcube/AC/releases/download/v1.2.0.2/AssaultCube_v1.2.0.2.tar.bz2"
+              <a href="../download.html"
               title="Linux">Linux</a>
             </td>
           </tr>

htdocs/download.html

@@ -89,6 +89,17 @@ <h3>Download Now:</h3>
             </td>
           </tr>
         </table>
+        <table id="downloadlink">
+          <tr>
+            <td>
+              <br>
+              <b>Note:</b> on older Linux systems with old libcurl3 and without newer libcurl4 library please download this
+              <a href="https://github.com/assaultcube/AC/releases/download/v1.2.0.2/AssaultCube_v1.2.0.2_libcurl3.tar.bz2">Linux client</a>,
+              supporting libcurl3 (it doesn't support libcurl4, so on newer Linux systems this client won't run, with the error:
+              <span class="code">libcurl.so.4: version `CURL_OPENSSL_3' not found</span> ).
+            </td>
+          </tr>
+        </table>
         <p>
           For installation guidance, read the <a href="docs/getstarted.html">getting started</a> guide
           in the AssaultCube documentation.