[krbdev.mit.edu #1364] make depend requires use of Gnu sed under Irix

[Ezra Peisach via RT]

Very low priority...

Trying to update dependencies failed to strip the the gcc include path
on an irix machine. Tracked it down to the Irix version of sed 
misbehaving and not outputting the gcc relevant lines....

Perhaps - do not allow updating of dependencies unless gnu's sed is
found... I have not evaluated which versions of sed are broken...

	 Ezra