[FIX] glLoadTransposeMatrixf

As reported by some, the glLoadTransposeMatrixf call fails on various  
Windows drivers (https://lists.wisc.edu/read/messages?id=850793).

Now we had the same problem on one machine here (some onboard  
graphics). Turns out this is due to an actual bug in loading the  
ARB_transpose_matrix extension functions - they were looking up the  
'glLoadTransposeMatrixf' symbol instead of 'glLoadTransposeMatrixfARB'.

Fix attached.

- Bert -