cleaned up file uploading error messages
fix for 0005346: misleading error message and inconsistent user interface
fix for 0004595: file upload in error report doesnt work
fix for 0004908: Missing error alert when file upload fails (Report Issue only)
fix for 0005282: Inappropriate error when Uploading a File without a file
fix for 0004857: Upgraded to 0.19.1 - DISK Upload failed - No error message
fix for 0004595: file upload in error report doesnt work

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3412 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9