Addressed all off Eli's and Tom's comments in the attached patch.

Thanks a lot Tom, for your detailed explanations.

2013-02-13  Siva Chandra Reddy  <sivachandra@google.com>

        Add a new method 'disassemble' to gdb.Architecture class.
        * python/py-arch.c (archpy_disassmble): Implementation of the
        new method gdb.Architecture.disassemble.
        (arch_object_methods): Add entry for the new method.

doc/

        * gdb.texinfo (Architectures In Python): Add description about
        the new method gdb.Architecture.disassemble.

testsuite/

        * gdb.python/py-arch.c: New test case
        * gdb.python/py-arch.exp: New tests to test
        gdb.Architecture.disassemble
        * gdb.python/Makefile.in: Add py-arch to the list of
        EXECUTABLES.