When sending a command with pwmd_command(), make sure than it is <=

When sending a command with pwmd_command(), make sure than it is <=
ASSUAN_LINELENGTH. If not, return GPG_ERR_LINE_TOO_LONG. This check is
done anywhere pwmd_command_ap() is used (_assuan_command() and
assuan_write_line() actually).

Call _pwmd_process() to parse any pending lines if pwm->state ==
ASYNC_DONE and in a command (ASYNC_CMD_OPEN/SAVE2).

Another fix for closing the remote connection when doing a
pwmd_open_async2() on a failure.

Check for GPG_ERR_ENOENT in _do_pwmd_save() after sending ISCACHED.

Fixed freeing the passphrase after writing to the pipe during a SAVE.

Code cleanups (libpwmd.c mainly).

Namespace cleanups.