gives $FSLDEVDIR precedence, and also allows a global override.

was always returning unknown. Also adjusted wx properties so they can be
queried if a gui is not open, but is available.

presence of 'mesa' or 'gallium' does not imply software rendering. And
llvmpipe is fast, so should be treated as hardware.

VNC-like environments.

previous commit.

using a software or hardware GL renderer.

initialisation. Async.idle still honours after argument, even if a
wx application is not running.

Platform.canHaveGui, can be used to tell whether we are able to create a
GUI. Async modified to use platform.haveGui instead of performing its
own test.

platform module.

we're running locally or over ssh.

log.memory .. all the __init__ stuff will make its way over to FSLeyes.

bug (http://trac.wxwidgets.org/ticket/16440) in FSLDIRDialog.

stuff to fsl.utils.platform