Explain better what each matching rule function means.

Explain better what each matching rule function means.
We need to indexing routines per matching rule.  One (cindex) is used to
create the indexes.  The other (sindex) is used to search.  This is
necessary because the syntax of the value assertion may be different
from the syntax of the attributes the matching rules is used with.
They may be the same function, however, and will be the same in most
cases.