Fix error in "last all" command and several -Wunused-result compiler errors (#55)

* Add build generated files to .gitignore

* Fix error in "last all" output and resolve Wunused-result warnings

- Check return value of several standard library calls that could
return error states.
- Fix issue with "last all" command (it sent tabs for alignment
that were reinterpreted as colors).

* Fix buffer overflow in do_export_zone command

.gitignore

@@ -1,3 +1,12 @@
 bin/*
 src/*.o
 src/util/*.o
+config.cache
+config.log
+config.status
+src/Makefile
+src/conf.h
+src/util/Makefile
+src/.accepted
+src/depend
+src/util/depend