More typo fixes across the tree

Previously I have made spelling changes as caught by Debian's lintian
tool, which has a short list of common misspellings that it tests for.
This time I decided to run codespell against the source and fix all the
obvious problems it came up with. It also uses a list of misspellings
but it's much larger than lintian's, but also has some false positives
so I went over the list by hand.

The command I used to do check the source was:
git ls-tree -rz --name-only HEAD | xargs -0 codespell -L minimise,errorstring

scripts/shairport-sync.in

@@ -47,7 +47,7 @@ do_start()
 {
 	# Return
 	#   0 if daemon has been started
-	#   1 if PID directory didn't exist and couldn't be created with approproate permission
+	#   1 if PID directory didn't exist and couldn't be created with appropriate permission
 	#   2 if daemon was already running
 	#   3 if daemon could not be started
         [ -e /var/run/shairport-sync ] || ( mkdir -p /var/run/shairport-sync && chown shairport-sync:shairport-sync /var/run/shairport-sync ) || return 1