hard-coded /sdcard/ fails on Samsung Galaxy

[danstowell]

We use hard-coded /sdcard/ because Environment.getExternalStorageDir() seemed wrong on some systems. However, on Samsung Galaxy the location is /external_sd/ so it fails.

For crossplatform, we might need to check both /sdcard/ and Environment.getExternalStorageDir(), and if either of those two seems to work then stick with it.

[misterinterrupt]

just a note that on Samsung Galaxy Tab ® S 10.5, it is the amazingly named /extSdCard/
afaik, /sdcard/ is just a dir on the tablet's internal flash