[BUG] canfar minor issues

[martinkilbinger]

Some bugs and issues have arisen from canfar runs; some quick-and-dirty hacks need to be fixed.

Major:

• job_sp_canfar.bash is killed sometimes when calling "command" (exit code 124, 136 or higher, message "killed $cmd").
  Only happens when called from curl, not when called on the portal directly or with init_*.sh.

MInor:

Modules:

• ME_* config entries: request "last:dir" or "all:dir" consistently.
• check mask runner for previous existing file (remove)

Scripts:

• prepare_tiles script: do both exp and tiles mask