git-resolve.sh: use the $( ... ) construct for command substitution

The Git CodingGuidelines prefer the $(...) construct for command
substitution instead of using the backquotes `...`.

The backquoted form is the traditional method for command
substitution, and is supported by POSIX.  However, all but the
simplest uses become complicated quickly.  In particular, embedded
command substitutions and/or the use of double quotes require
careful escaping with the backslash character.

The patch was generated by:

for _f in $(find . -name "*.sh")
do
   sed -i 's@`\(.*\)`@$(\1)@g' ${_f}
done

and then carefully proof-read.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/examples/git-resolve.sh

@@ -75,7 +75,7 @@ case "$common" in
 		GIT_INDEX_FILE=$G git read-tree -m $c $head $merge \
 			2>/dev/null || continue
 		# Count the paths that are unmerged.
-		cnt=`GIT_INDEX_FILE=$G git ls-files --unmerged | wc -l`
+		cnt=$(GIT_INDEX_FILE=$G git ls-files --unmerged | wc -l)
 		if test $best_cnt -le 0 -o $cnt -le $best_cnt
 		then
 			best=$c