Enhance plugin version dependency checking.
Rather than a simple string comparison, do a smart string explode and check individual version bits.
Also allows plugins to now specify a 'maximum' version, where a plugin will only work with dependency versions lower than specified.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@4793 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9