Log Message:
Select fields explicitly from df.depends in make.df.depends().

The function make.df.depends() constructs a dataframe for DEPENDS lines in
the updated Makefile.  That dataframe is combined with other dataframes for
different portions of the Makefile.  Consequently, all the dataframes must
have the same fields or combining with rbind() fails.  Previously, the
dataframe had the wrong set of fields; this explicitly selects the correct
set that matches the other dataframes so that they can all be combined
correctly.