Seems like there could be a defect in uClibc making errno not
thread-local. Don't rely on errno value but check function return value
instead which is a better failure indicator.
Return errors from `tr_loadFile` and `tr_variantFromFile` via tr_error.
Fix `tr_sessionLoadSettings` to not fail on Windows if settings.json
does not exist.
Remove unused `renamed` argument.
Use tr_error instead of errno to report errors to support Win32 file
wrappers which do not map Windows error codes to POSIX ones.
Return bool instead of int (0/-1).
Uncomment tr_error_prefix and tr_error_propagate_prefixed functions.
Additionally,
* always close file descriptor on error in cached_file_open (FD leak),
* only store file descriptor to tr_cached_file on success,
* call ftruncate after xfsctl-based preallocation so that correct size
is reported by the system.
Mike Gelfand