Fix GDB tab completion issue

So it seems that importing readline causes issue with the GDB prompt, in fact
GDB already tries (failing) to avoid that. The issue manifests when debugging a
program with the source code available, e.g., C, and IPython is available in the
system.

Close #325, #326

.gdbinit

@@ -2374,6 +2374,11 @@ set python print-stack full
 
 python Dashboard.start()
 
+# Fixes ------------------------------------------------------------------------
+
+# workaround for the GDB readline issue, see #325
+python import sys; sys.modules['readline'] = None
+
 # File variables ---------------------------------------------------------------
 
 # vim: filetype=python