Allow unrar to overwrite files

On systems without the appropriate 7zip functionality, corrupt files will be created in the working directory, causing unrar to fail as its default behavior is to disallow overwriting files with the same names.

kindlecomicconverter/comicarchive.py

@@ -57,7 +57,7 @@ class ComicArchive:
                         self.filepath + '"', stdout=PIPE, stderr=STDOUT, stdin=PIPE, shell=True)
         process.communicate()
         if process.returncode != 0:
-            process = Popen('unrar x -y -x__MACOSX -x.DS_Store -xthumbs.db -xThumbs.db "' + self.filepath + '" "' +
+            process = Popen('unrar x -y -o+ -x__MACOSX -x.DS_Store -xthumbs.db -xThumbs.db "' + self.filepath + '" "' +
                     targetdir + '"', stdout=PIPE, stderr=STDOUT, stdin=PIPE, shell=True)
             process.communicate()
             if process.returncode != 0: