ByteArray: Add some tests for methods returning self.

* tests/Makefile.am:
* tests/glibmm_bytearray/main.cc: New file with tests. These are
failing now.
ByteArray: Fix refcount problems.

* glib/src/bytearray.hg: Add refreturn to methods returning self.
.gitignore: Update.

* .gitignore: Ignore the files generated by Automake testing
infrastructure.