Allow for TRE size differences caused by version number in tests.
The TRE section size contains the svn version number. This varies depending
on whether your checkout is modified or not.  So allow the size to differ by
a couple of characters before throwing a failure.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2646 25d90789-57f7-4ee0-8453-03a3dfeeeb22