test-fetch: fix non-portable sed regex.

(s/...\+/.../ appears to be a GNU-ism: this test broke on OS X and
NetBSD.  Changing \+ to * fixes it, although that is a slightly less
strict regex.)

tests/test-fetch

@@ -194,7 +194,7 b' echo b > i1726r1/a'
 hg --cwd i1726r1 ci -m second
 echo c > i1726r2/a
 hg --cwd i1726r2 ci -m third
-HGMERGE=true hg --cwd i1726r2 fetch ../i1726r1 | sed 's/new changeset 3:[0-9a-zA-Z]\+/new changeset 3/'
+HGMERGE=true hg --cwd i1726r2 fetch ../i1726r1 | sed 's/new changeset 3:[0-9a-zA-Z]* /new changeset 3 /'
 hg --cwd i1726r2 heads default --template '{rev}\n'
 
 "$TESTDIR/killdaemons.py"