strarray: we should dispose instead of free

We _dispose_ the contents of objects; we _free_ objects (and their
contents).  Update `git_strarray_free` to be `git_strarray_dispose`.
`git_strarray_free` remains as a deprecated proxy function.

examples/checkout.c

@@ -239,7 +239,7 @@ next:
 
 out:
 	git_reference_free(remote_ref);
-	git_strarray_free(&remotes);
+	git_strarray_dispose(&remotes);
 	return error;
 }
 

examples/general.c

@@ -707,7 +707,7 @@ static void reference_listing(git_repository *repo)
 		git_reference_free(ref);
 	}
 
-	git_strarray_free(&ref_list);
+	git_strarray_dispose(&ref_list);
 }
 
 /**

examples/remote.c

@@ -129,7 +129,7 @@ static int cmd_rename(git_repository *repo, struct remote_opts *o)
 		puts(problems.strings[0]);
 	}
 
-	git_strarray_free(&problems);
+	git_strarray_dispose(&problems);
 
 	return retval;
 }
@@ -207,7 +207,7 @@ static int cmd_show(git_repository *repo, struct remote_opts *o)
 		git_remote_free(remote);
 	}
 
-	git_strarray_free(&remotes);
+	git_strarray_dispose(&remotes);
 
 	return 0;
 }

examples/tag.c

@@ -162,7 +162,7 @@ static void action_list_tags(tag_state *state)
 		each_tag(tag_names.strings[i], state);
 	}
 
-	git_strarray_free(&tag_names);
+	git_strarray_dispose(&tag_names);
 }
 
 static void action_delete_tag(tag_state *state)