Use xrealloc instead of realloc

Use xrealloc instead of realloc

Change places that use realloc, without a proper error path, to instead use
xrealloc. Drop an erroneous error path in the daemon code that used errno
in the die message in favour of the simpler xrealloc.

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>