fix test-strip-cross on solaris

fix test-strip-cross on solaris

Apparently "ENVVAR=value command" doesn't work when command is a shell
function.

Reported by Richard Lowe.

--- a/tests/test-strip-cross	Mon Jan 21 14:15:38 2008 +0100
+++ b/tests/test-strip-cross	Mon Jan 21 13:37:27 2008 -0200
@@ -43,7 +43,8 @@
 
 commit '201 210' '021 120' '012 102'
 
-HGUSER=another-user commit 'manifest-file'
+HGUSER=another-user; export HGUSER
+commit 'manifest-file'
 
 commit '012' 'manifest-file'