Enhancement 0001088: formatting of text in bugnotes, description areas.

Given that PRE tag is not used for bugnotes as well as other fields like summary / additional information, ...etc, the spaces at the beginning of the lines were lost. Hence, if the user typed code, it will be displayed without any indentation. This commit fixes this problem by retaining these spaces without using the PRE tag. One disadvantage of PRE tag is that it disables wrapping.

M core/string_api.php

• (string_preserve_spaces_at_bol): Added to preserve spaces at the beginning of lines by changing spaces to nbsp.
• (string_display): Changed to call string_preserve_spaces_at_bol()

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2375 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9