Correct common spelling mistakes in comments and tests

Most of these were found using Lucas De Marchi's codespell tool.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-add--interactive.perl

@@ -1247,7 +1247,7 @@ sub summarize_hunk {
 
 
 # Print a one-line summary of each hunk in the array ref in
-# the first argument, starting wih the index in the 2nd.
+# the first argument, starting with the index in the 2nd.
 sub display_hunks {
 	my ($hunks, $i) = @_;
 	my $ctr = 0;