Fix a problem that truncated mdb_doc files.

util/info_to_doc.c:
    Fix a problem that caused the generation of truncated mdb_doc files,
    and from that truncated test/debugger/mdb_command_test.inp files.
    The problem was that this program expected the info program to quote
    the initial line of each mdb command like this:

        `cmdname options ...'

    but on some machines, including mine, it quotes them like this:

        'cmdname options ...'

    i.e. with the initial as well as the final quote being a forward quote.
    This program now accepts either.

util/Mmakefile:
    Fix white space.

doc/generate_mdb_doc:
    Fix inconsistent indentation. Protect shell variable references.

doc/Mmakefile:
    Generate an error message if a similar problem occurs again
    when creating mdb_doc.

    Fix indentation.

tools/bootcheck:
    Generate an error message if a similar problem occurs again
    when copying tests/debugger/mdb_command_test.inp.