CONFIG sets up the code fuses for the micro like brown out detect,
internal oscilator etc

I think CBLOCK sets up RAM but could be wrong its a while since i used
it.

a) CONFIG/CBLOCK directive: I don't know what these
directives do

b) retfie dt; this is a Pic18 instruction. But, mplab
uses only "retfie". Is it equivalent to "retfie 0"?

If I comment these directive, then my files are
compiled. But, the hex files are not same. Also, mplab
generated hex files are not in previous (pic16fx) format. The
header is in previous format. But, the body is broken
in many small lines rather than few wide lines. Is it
due to the new directives?

Thanks