Refactored TestCasePackager.ps1 such that it now produces test case XMLs according

to the following criteria:
1.  If a test case directory directly contains *.js files at the root level, package
    the entire directory as an XML regardless of how many *.js files are in
    subdirectories
2.  If the directory and subdirectories contain less than 1,000 test cases, package
    the entire directory as an XML.  Otherwise...
3.  Perform steps 1 and 2 on each subdirectory of the directory

The net effect of this change is that no test case XMLs are larger than 1.5 megs any longer,
although the total number of test XMLs has jumped from about a dozen to ~75.  This should
make running the test harness seem a little smoother across all browsers since we won't be
blocked downloading 4 meg files for several seconds any longer.