[MERGE][0.16] temp file for commit message in external editor should be opened in text mode (#110901)

[John Arbash Meinel]

John Arbash Meinel has voted +1.
Status is now: Approved
Comment:
I know we generally avoid using local vars because it can sometimes 
obscure the test. (What function are you using???). However, in this 
case, I think it aids clarity, and it is used right away.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C46370558.3080204%40ukr.net%3E