Prevent cancelquery() from starting the statemachine.
This was responsible for the majority of the exceptions.

Also destruct the conxion object directly, to make sure that the
filedescriptors actually get closed.

This reverts commit f339d7f8.

The kludge should not be needed anymore due to a checked in fix
in the Pike compiler.

As reported by Jeff Hungerford:

When there is:
- No connection at present.
- Two or more threads try to open an initial connection to the database
  simultaneously.

You can trigger this:

Attempting to clone an unfinished program
/usr/local/pike/8.0.175/lib/modules/Sql.pmod/Sql.pike:342:
    Sql.Sql()->create("localhost:5432","foo","bar","CENSORED",UNDEFINED)

This could be caused by a race in the Pike-core class-cloning code which
is not racefree when two threads try to instantiate the same object
at roughly the same instant.

This patch attempts a workaround to detect the race and loop until
it finishes without problems.  It would be better if this could be
fixed in the Pike-core.