git-fetch.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-fetch.sh

@@ -67,7 +67,7 @@ do
 		keep='-k -k'
 		;;
 	--depth=*)
-		shallow_depth="--depth=`expr "z$1" : 'z-[^=]*=\(.*\)'`"
+		shallow_depth="--depth=$(expr "z$1" : 'z-[^=]*=\(.*\)')"
 		;;
 	--depth)
 		shift
@@ -262,12 +262,12 @@ fetch_per_ref () {
       http://* | https://* | ftp://*)
 	  test -n "$shallow_depth" &&
 		die "shallow clone with http not supported"
-	  proto=`expr "$remote" : '\([^:]*\):'`
+	  proto=$(expr "$remote" : '\([^:]*\):')
 	  if [ -n "$GIT_SSL_NO_VERIFY" ]; then
 	      curl_extra_args="-k"
 	  fi
 	  if [ -n "$GIT_CURL_FTP_NO_EPSV" -o \
-		"`git config --bool http.noEPSV`" = true ]; then
+		"$(git config --bool http.noEPSV)" = true ]; then
 	      noepsv_opt="--disable-epsv"
 	  fi