iostream-temp: If write() to temp file fails at any time, move it back to memory. Similarly to if the write() to temp fails during the initial move attempt. This way even if write() fails due to out of disk space, it's not visible to caller. An error message is logged in any case.

lib: Added iostream_temp_create_sized() to specify the max in-memory size

lib: Added iostream_temp_create_named()

iostream-temp: Avoid copying data if IOSTREAM_TEMP_FLAG_TRY_FD_DUP is set.

Added iostream-temp for easily creating a temporary istream (to memory/file).