Speeding up debugger check (addresses #64)

Speeding up debugger check (addresses #64)

Soooo, the long delay experienced when evaluating long string lists in
Guile had nothing to do with the time took by emacs to read the response
from the scheme process; that process is always a breeze, no matter or
its format or number of newlines.  The delay was provoked by an innocent
looking function that scans the received string (which includes a prompt
at the end as an EOT marker) to check whether Guile (or any other
scheme) has just entered the debugger (that's done inside
`geiser-con--connection-update-debugging`).  For some reason,
`string-match` on that kind of string using Guile's regexp for a debug
prompt takes forever.  Instead of trying to optimize the regular
expression, i've just applied it to the *second* line of the received
string, which is the one that contains the response's prompt.