Change path search order in GetSubversionPath to fix issue with SVN 1.7.9

Move check for /opt/subversion/bin/svn first. Nicolas Cottaris in my
lab says this fixes a problem that arose when he installed SVN 1.7.9.
It is possible that this will break for some other version, so we
should keep an eye on it.
Expanding comments, no functinal changes.  DHB
Further testing of Z136 implementation.

1) Carefully checked values in AnsiZ136MPEDeloriTestInput.txt to make sure they matched what Delori's Excel spreadsheet produces.  They do.

2) Worked through the two cases where there are discrepancies between the PTB code here and the spreadsheet and discovered that the problem is in the value of T2 used.  My reading of the standard is that the PTB code here is correct.  Added comments to this effect in the test code, and added two Word documents that work through the calculations by hand to this repository.  Emailed Delori to see if he has insight about why his spreadsheet uses a different value for T2.

Signed-off-by: David Brainard <brainard@psych.upenn.edu>
Cosmetic only.

Signed-off-by: David Brainard <brainard@psych.upenn.edu>
Merge pull request #118 from kleinerm/master

PTB BETA RELEASE "Rainbows, Droids & Compute Hippies!" SP4
Merge pull request #119 from kleinerm/master

DAQ toolbox fixes.
Merge pull request #25 from Psychtoolbox-3/master

Resync with current master of official Psychtoolbox-3 repo.