This patch adds the mechanism for gdb to respond to "matrix" hints from 
printers.py.  (Just to exercise the testcase, the patch includes a 
patched version of printers.py to src/gdb/testsuite/gdb.python.  It can 
be removed once the patched printers.py is generally available.)

Question:  pr10659.exp yields:

    +ERROR: no fileid for qcore
    +ERROR: Couldn't send python print 'test' to GDB.
    +UNRESOLVED: gdb.python/pr10659.exp: verify python support

The actual tests pass, but I haven't the slightest idea how to get rid 
of those errors or even if it's necessary to do so.

-cm