Add missing checks and fix hexdump output (closes #878)

dehydrated

@@ -260,7 +260,7 @@ _mktemp() {
 # Check for script dependencies
 check_dependencies() {
   # look for required binaries
-  for binary in grep mktemp diff sed awk curl cut; do
+  for binary in grep mktemp diff sed awk curl cut head tail hexdump; do
     bin_path="$(command -v "${binary}" 2>/dev/null)" || _exiterr "This script requires ${binary}."
     [[ -x "${bin_path}" ]] || _exiterr "${binary} found in PATH but it's not executable"
   done
@@ -839,7 +839,7 @@ hex2bin() {
 
 # Convert binary data to hex string
 bin2hex() {
-  hexdump -e '16/1 "%02x"'
+  hexdump -v -e '/1 "%02x"'
 }
 
 # OpenSSL writes to stderr/stdout even when there are no errors. So just