Refactor internals of config_ex.  This turns unnecessary arguments
into flags.

Further, make sure that we never call abort or exit if configuration
fails -- there were still a few cases where this could happen when
the user requests to disable this behavior.
Fix cases where parameter defaults were not valid values for the
specified type (for example, a boolean value which defaulted to
"peer").
Fix macro implementation for param table.

The result of PARAM_TABLE_QUOTEME(foo) was the token "foo"; one
needs a second macro so we can first expand foo to its value, then
stringify the value.

This caused HAVE_EXT_KRB5 to default to "HAVE_EXT_KRB5" when it was
defined instead of the desired "1".
Make the htcondor.param object more dictionary-like

In particular, I added keys, update, items, __len__, __iter__, and
__contains__.