Replace deprecated str2mat() by char() in some M-Files.

Unsupported by stock Octave-3.6.2, deprecated by Matlab.
-> Makes RenderDemo work on Octave.
Screen/Linux: Fix missing glibconfig.h on some 64-Bit builds.

Building on Ubuntu 12.10 with 64-Bit Octave/Matlab results in
complaints about missing glibconfig.h, because it is no longer
stored in the i386-linux-gnu subfolder, but the x86_64-linux-gnu
subfolder. Makes sense for a 64-Bit build.

Add an extra include for that path, so gcc looks in both locations.
-> Screen for 64-Bit Octave rebuilt and tested.
Screen/Linux: Fix most compiler warnings.

Except the ones we can't avoid due to backwards compat needs.
Screen/Linux: Remove nouveau boilerplate warning.

Nouveau, as of version 1.0.0, released 18th June 2012, is
no longer a hazard for visual stimulus timing. It should
provide accurate/robust stimulus onset timing. Stimulus
onset timestamping should be reliable and robust. Accuracy
of onset timestamps is still not as great as it could be
due to lack of high precision support in the nouveau-kms
kernel driver as of Linux 3.9, februrary 2013. However,
accuracy is comparable to what other vision science toolkits
would achieve and good enough for light to medium precision
needs, about 1 msec. Usercode can switch to high precision
by using Screen('Preference','VBLTimestampingmode', 1); if
needed. This (plus the usual amount of tinkering with display
mappings on non-standard display setups) would use the
high-precision beamposition timestamping as with the
proprietary NVidia binary blob.

Anyway, do away with the warning boilerplate, it is no
longer justified.