1) replaced characters arrays with class BString through the whole
program. The string formatting code has become much cleaner.
2) class Util returns error message via CString instead of character
buffers.
3) few more places to use CString.
Before scanning of dupe directories the directories are quickly checked
by dupe matcher. It determines if they contain or may contain the same
content. If the dupe checker detects a dupe containing different
content as the download being currently processed by par-checker, such
extra dupe is skipped to save time during dupe par scan.
