Update comments to make behavior clearer
Update comments to make behavior clearer

Added comment to Mat_Error that mat_log calls abort and does not return.

Fix Mat_Help comment to indicate correct return value.

tbeu/matio,MaartenBent/matio,MaartenBent/matio,NJannasch/matio,NJannasch/matio,tbeu/matio,tbeu/matio,MaartenBent/matio,MaartenBent/matio,tbeu/matio