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.
% test issue352
adding he
llo
abort: '\n' and '\r' disallowed in filenames: 'he\rllo'
adding he
llo
abort: '\n' and '\r' disallowed in filenames: 'he\rllo'
adding hell
o
abort: '\n' and '\r' disallowed in filenames: 'hell\no'
adding hell
o
abort: '\n' and '\r' disallowed in filenames: 'hell\no'
f he
llo he
llo
f hell
o hell
o
% test issue2039
[0;35;1;4m? foo[0m
[0;35;1;4mbar[0m
[0;35;1;4m? foo[0m
[0;35;1;4mbar.baz[0m