MainWindow.java: Updated window and component behavior; main window is
no longer resizable, browse button can be selected by the mnemonic
Alt+B.

ProgressWindow.java: Updated window default values; window title now
includes the target folder. Implemented abort button behavior.

FileIndex.java: Bug fixed; FileIndex's merge method was broken because
the contains() call was calling the contains() method belonging to the
encapsulated ArrayList of HashableFile objects instead of FileIndex's
contains() method. This bug was causing file's with paths that qualified
for two or more inclusive filters to be listed twice or more, rather
than excluded by the merge() call.