Support java.io.File#lastModified not only on Windows

There was already non-Windows support, but it was put into the
Windows-specific part. Move it outside.

While at it, change the left-over 'st' to 'fileStat' to fix the
compilation.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure to test java.io.File#lastModified

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #81 from dscho/last-modified

Fix unsatisfied link error when calling java.io.File#lastModified on non-Windows