Light wysiwyg integration :)

In condition to issue #1293476: How to combine GeSHi Filter with Wysiwig module (TinyMCE editor) ?.
We can manually tune GeSHi Filter for use with wysiwyg editors:
1. Only one tag is allowed for filter - <pre>
2. Turn off any html validation in wysiwyg editors setting.
3. Insert your code in editor textarea as <pre> tag in form <pre start="1" linenumbers="normal" type="my language" title="My title"> or use http://drupal.org/sandbox/victor_gamedev.by/1270766 module.
4. Edit geshifilter.pages.inc file. In function geshifilter_geshi_process() add after

  // remove leading/trailing newlines
  $source_code = trim($source_code, "\n\r"); 

this lines

  // fix: Replace any HTML specials
  $source_code = str_replace(">", ">", $source_code);
  $source_code = str_replace("&lt;", "<", $source_code);
  $source_code = str_replace("&lsaquo;", "‹", $source_code);
  $source_code = str_replace("&rsaquo;", "›", $source_code);
  $source_code = str_replace("&#39;", "'", $source_code);
  $source_code = str_replace("&quot;", "\"", $source_code);
  $source_code = str_replace("&amp;", "&", $source_code); 

that's all.