Import xmatrial hang

[J.D. Laurence-Chasen]

If my machine runs out of disk space while importing an xmatrial file, XMALab doesn't seem to notice, and hangs. (On a windows 10 pc)

[Benjamin Knorlein]

fixes #49 : Added an error message when it cannot write to the file due to diskspace issues

→ <<cset ee2e9a677764>>