IOW, be nice with the OS and other software/users.

- /tmp should never be hardcoded: $TMPDIR is better
- $TMPDIR should be only used with 'tempfile' and appropriate clean up
- in unit tests, the 'tests' directory can be used as temporary storage
  (like in this commit)

This fixes possible random failures of SyncML related tests when, for example,
testERP5SyncML and testERP5DocumentSyncML are run in parallel.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@34864 20353a03-c40f-0410-a6d1-a30d3c3de9de