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.

--- a/tests/test-convert-hg-svn.t	Tue Mar 15 14:10:46 2016 -0700
+++ b/tests/test-convert-hg-svn.t	Tue Mar 15 00:14:53 2016 +0900
@@ -1,7 +1,7 @@
 #require svn svn-bindings
 
   $ filter_svn_output () {
-  >     egrep -v 'Committing|Updating' | sed -e 's/done$//' || true
+  >     egrep -v 'Committing|Updating|(^$)' | sed -e 's/done$//' || true
   > }
 
   $ cat <<EOF >> $HGRCPATH

--- a/tests/test-convert-svn-source.t	Tue Mar 15 14:10:46 2016 -0700
+++ b/tests/test-convert-svn-source.t	Tue Mar 15 00:14:53 2016 +0900
@@ -1,7 +1,7 @@
 #require svn svn-bindings
 
   $ filter_svn_output () {
-  >     egrep -v 'Committing|Updating' | sed -e 's/done$//' || true
+  >     egrep -v 'Committing|Updating|(^$)' | sed -e 's/done$//' || true
   > }
 
   $ cat >> $HGRCPATH <<EOF

--- a/tests/test-subrepo-svn.t	Tue Mar 15 14:10:46 2016 -0700
+++ b/tests/test-subrepo-svn.t	Tue Mar 15 00:14:53 2016 +0900
@@ -8,7 +8,7 @@
 #endif
 
   $ filter_svn_output () {
-  >     egrep -v 'Committing|Transmitting|Updating' || true
+  >     egrep -v 'Committing|Transmitting|Updating|(^$)' || true
   > }
 
 create subversion repo
@@ -97,10 +97,8 @@
   committing subrepository s
   Sending*s/alpha (glob)
   Committed revision 3.
-  
   Fetching external item into '*s/externals'* (glob)
   External at revision 1.
-  
   At revision 3.
   $ hg debugsub
   path s