unset $HOME variable under Linux - scripts autoload fails

[c.statkiewicz]

 Hi,

 I'm running PhotoScan in a bit restricted environment, which causes that $HOME env var might be not set (it's not a feature of this env, just unexpected side effect; also non-standard home dir is used). I've noticed that this will affect PhotoScan behavior:
 * there will be \~/.agisoft directory created (yes, tilde named dir) in current work dir, instead of home dir,
 * script autoloading will fail - no script will be loaded.

 The fix is setting up $HOME env obviously, but I also suggest more strict checking of runtime environment, and at least leaving some message in logs about unset env vars and/or unreadable paths with configuration. This will help debugging similar problems in the future.