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.
#!/usr/bin/env python
#
# This used to be a simple sed call like:
#
# $ sed "s:$HGTMP:*HGTMP*:"
#
# But $HGTMP has ':' under Windows which breaks the sed call.
#
import sys, os
input = sys.stdin.read()
input = input.replace(os.sep, '/')
hgtmp = os.environ['HGTMP'].replace(os.sep, '/')
input = input.replace(hgtmp, '$HGTMP')
sys.stdout.write(input)