examples: avoid warning when iterating over index entries

When iterating over index entries, we store the indices in an unsigned
int. As the index entrycount is a `size_t` though, this may be a loss of
precision which a compiler might rightfully complain about.

Use `size_t` instead to fix any warnings.

examples/general.c

@@ -624,7 +624,7 @@ static void revwalking(git_repository *repo)
 static void index_walking(git_repository *repo)
 {
 	git_index *index;
-	unsigned int i, ecount;
+	size_t i, ecount;
 
 	printf("\n*Index Walking*\n");
 

examples/show-index.c

@@ -17,7 +17,7 @@
 int lg2_show_index(git_repository *repo, int argc, char** argv)
 {
 	git_index *index;
-	unsigned int i, ecount;
+	size_t i, ecount;
 	char *dir = ".";
 	size_t dirlen;
 	char out[GIT_OID_HEXSZ+1];