tests: Don't use $PWD stable

tests: Don't use $PWD

$PWD doesn't work with solaris sh - use `pwd` instead

--- a/tests/test-convert-p4-filetypes	Wed Jan 20 23:23:18 2010 +0100
+++ b/tests/test-convert-p4-filetypes	Fri Jan 22 17:13:55 2010 +0100
@@ -6,7 +6,7 @@
 echo "convert = " >> $HGRCPATH
 
 echo % create p4 depot
-P4ROOT=$PWD/depot; export P4ROOT
+P4ROOT=`pwd`/depot; export P4ROOT
 P4AUDIT=$P4ROOT/audit; export P4AUDIT
 P4JOURNAL=$P4ROOT/journal; export P4JOURNAL
 P4LOG=$P4ROOT/log; export P4LOG