sometimes xUnique did not sort when do both uniquifying and sorting

[truebit]

• Without any argument, xUnique do both unique and sort. when used by a pre-commit hook, it worked as below:

Uniquify and Sort
Ignore uniquify, no changes made to /Users/test/Documents/test/Test.xcodeproj
Ignore sort, no changes made to /Users/test/Documents/test/Test.xcodeproj
Uniquify and Sort done

• Actually the project file needs to be sorted and xUnique did not sort it;
• When using -s alone to sort, sorting works fine.

Cause: unique and sort using the same .bak filename, it may exist conflict. After change different backup file name for sorting and uniquifying, it works without conflicts