Fix rbt patch with unicode characters.
rbt patch was completely failing with unicode characters, presenting

errors on the console. We now encode thet content before writing it to a

temp file, and decode before feeling it to 'git commit'.

Created a change with unicode characters, and successfully applied it.
Verified the characters appeared in my editor and in the resulting commit

message.
Previously, this was breaking at two points: When it tried to run the editor,

and when it tried to create the commit from the editor's contents.