rename "set debugvarobj" to "set debug varobj"

I think "set debugvarobj" has the wrong name.
It ought to be "set debug varobj", like gdb's other debug settings.

This patch makes the change.

I chose not to install deprecated aliases, since this is only a debug
setting; but if someone feels strongly about it I will add them.

Built and regtested on x86-64 Fedora 20.

2014-04-29  Tom Tromey  <tromey@redhat.com>

	* varobj.c (_initialize_varobj): Rename to "set debug varobj" and
	"show debug varobj".

2014-04-29  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Debugging Output): Rename to "set debug varobj" and
	"show debug varobj".