ac_check_krb5 - comments requested

[Tom Yu]

I've checked in a preliminary example autoconf macro for using
krb5-config (both MIT and Heimdal) for setting build system paramters
for building applications.  I have a few points on which I would like
comments.

(1) Should it set LIBS rather than LDFLAGS (I am leaning towards yes)

(2) What should be done about runpaths?  (In MIT krb5, they are
    currently emitted if the build system linked the krb5 binaries
    with runpaths.)  Note that actually altering current behavior
    might break some things, and requires altering krb5-config's
    behavior in any case.

(3) Related to (2), what should be done about differences between
    compilers on the same platform?

---Tom