Rename --partsize to --part-size for consistency with other options

ia-upload-stream

@@ -399,7 +399,7 @@ def main():
 		return o
 
 	parser = argparse.ArgumentParser()
-	parser.add_argument('--partsize', dest = 'partSize', type = size, default = size('100M'), help = 'size of each chunk to buffer in memory and upload (default: 100M = 100 MiB)')
+	parser.add_argument('--part-size', '--partsize', dest = 'partSize', type = size, default = size('100M'), help = 'size of each chunk to buffer in memory and upload (default: 100M = 100 MiB)')
 	parser.add_argument('--no-derive', dest = 'queueDerive', action = 'store_false', help = 'disable queueing a derive task')
 	parser.add_argument('--clobber', dest = 'keepOldVersion', action = 'store_false', help = 'enable clobbering existing files')
 	parser.add_argument('--ia-config-file', dest = 'iaConfigFile', metavar = 'FILE', help = 'path to the ia CLI config file (default: search the same paths as ia)')