Avoid hangs when process with embedded connection goes into stopped state.

[AlexPeshkoff]

If user accidentally hits ctrl-z in any embedded firebird application (putting it therefore into stopped state) some important database operations like CREATE DATABASE fail to execute and fail with "Timeout when waiting callback from other process" message.

Issue was reported by Paulius Pazera paulius.pazera@glds.com.

Hang when process with embedded attachment is stopped is kind of normal behavior. To avoid it - desired solution is handle SIGTSTP and avoid going into stopped state.