fix bash completion of filenames containing spaces

Work around https://github.com/pcapriotti/optparse-applicative/issues/146
by not using action "file" and instead passing -o bashdefault -o default
to complete. This way, when optparse fails to complete a filename, bash
will fall back to regular filename completion.

Unfortunately, optparse-applicative does not provide a way to control the
options passed to complete, so I had to modify its generated completion script.

Note that for "git annex" command completion, git's completion script already
used -o bashdefault -o default, so that works too.

CmdLine/GitAnnex/Options.hs

@@ -89,8 +89,6 @@ gitAnnexGlobalOptions = commonGlobalOptions ++
 cmdParams :: CmdParamsDesc -> Parser CmdParams
 cmdParams paramdesc = many $ argument str
 	( metavar paramdesc
-	-- Let bash completion complete files
-	<> action "file"
 	)
 
 parseAutoOption :: Parser Bool