Changed code in csv_conv() to use iconv() if it exists when converting output for CSV files because it's faster.  Also fixed a bug whereby if iconv() was being used it added a BOM when one wasn't needed because csv_conv() is only used to convert partial strings and not a complete file.   See also SF Support Requests #585.

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2861 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7