tests: don't match blank output lines as regexes in unified tests
Currently, the following unified test will pass:
$ echo foo
A blank output line (a line containing just two spaces) will match any
output.
The patch modifies the unified test runner to ignore empty strings
strings when do regular expression matching.
[ original upstream message ]
syntax: glob
*.pyc
*.pyo
*~
*.swp
*.orig
*.rej
.DS_Store
build/*
MANIFEST