Parser message for `index` files with unrecognized options is misleading

[mgduda]

The parser for the index file for geogrid datasets reports unrecognized options according to the position of the = character in the line, rather than the line number (which would be much more helpful). For example, the index file

type = continuous
signed = yes
projection = regular_ll
dx = 0.00027777778
dy = 0.00027777778
known_x = 1.0
known_y = 1.0
known_lat = 31
known_lon = 100
wordsize =2
endian = little
tile_x = 3601
tile_y = 3601
tile_z = 1
row_order=top_bottom
missing_value = 32768
units = "meters MSL"
description = "ASTER 1-sec Topography Height"
foobar=6

gives the error message

WARNING: In /home/wrf/geog/topo_ASTER/index, unrecognized option  in entry 7.

.