tests: make tests for convert with svn portable...
tests: make tests for convert with svn portable
svn 1.6.x (at least, 1.6.12 or 1.6.17) might display empty lines, even
though svn 1.9.x (at least, 1.9.3) doesn't.
To make tests for convert with svn portable, this patch adds "|(^$)"
regexp to egrep in filter_svn_output.
To avoid similar future issue, this patch adds "|(^$)" regexp to all
filter_svn_output (and adjusts test-subrepo-svn.t), even though only
test-convert-svn-source.t fails with svn 1.6.x, AFAIK.