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

alac.h

@@ -13,7 +13,7 @@ void alac_free(alac_file *alac);
 
 struct alac_file {
   unsigned char *input_buffer;
-  int input_buffer_bitaccumulator; /* used so we can do arbitary
+  int input_buffer_bitaccumulator; /* used so we can do arbitrary
                                       bit reads */
 
   int samplesize;