Fix incorrect Status -> Error rename in IOHandler

Change 302872 was a massive rename of the Error class to Status.

The change included an incorrect rename of the "Status" window
in the LLDB GUI from "Status to "Error". This patch undoes this incorrect
rename and restores the status window's correct name.

Differential Revision: https://reviews.llvm.org/D33241
Patch by Brian Gianforcaro.

llvm-svn: 303553