Update Avxsynth header

Inclusion of assert.h has been moved from the avxsynth namespace, which
is important for my upcoming regression test executable.
Add testing of TurnsTile/CLUTer error messages

Using Phil Nash's Catch framework; only testing error handling for
now, output will have to wait a while.
Restructure test directories

Include directives updated accordingly.
Switch error tests from hardcoded strings to generated reference data

Also bring Catch up to latest revision, break some code out into
functions. Test scripts and reference data will be added in a separate
commit, to make actual code changes easier to see.
Add test scripts and current reference data

Addition of these files kept separate from previous commit to make
viewing code changes easier.
Make CompareData give more useful error message
Remove old mode range reference file

Shouldn't have been commit to begin with, was rendered obsolete by
commit 7fc5658
Remove AsClip call from Invoke in ImportScriptAvs

Stupid mistake; forcing the result of Invoke into clip form means any
subsequent calls to AVSValue type checking functions can't be trusted.
Add RunTestAvs function
Add first output tests, for tilew and tileh

Test scripts and reference data forthcoming.
Add scripts and reference data for previous commit
Improve fallback message in RunTestAvs

Provides the script name in cases where the result of evaluation isn't a
string or clip. The alternative would be an unwieldy number of test
cases and/or sections.
Add test for res parameter
Add scripts and reference data for res test
Fix TV levels tilesheet processing

Somehow I ended up with the wrong formula for range scaling.
Add test case for levels parameter
Add scripts and reference data for levels test
Stop test code from catching Avisynth exceptions
Add filename to test output when results change

In commit d3551b8 I added the script name to the output when a test
failed to evaluate a script, but I didn't account for successfully
processed scripts that simply differ from the previous result.
Fix frame hashing to account for planar frames