[PATCH] Disable bracketed paste mode in GDB tests

[Tom Tromey]

Andreas> Perhaps it's specific to bash.

Andreas> $ INPUTRC=/tmp/inputrc bash
Andreas> readline: /tmp/inputrc: line 1: foo: unknown variable name

Hmm.  I do see this with the system gdb:

    readline: /tmp/INP: line 1: foo: unknown variable name

I wonder why I don't see it with the gdb I built.
Maybe I need to try a system readline build.

Also I am not sure about the $if solution, given that readline 8.1 has a
bug here.  We can fix that in-tree, but that fix won't work for a system
readline build.  Ugh.

Tom