[xml] gethrtime and *Timer

[Rick Jones <rick jones2 hp com>]

I'm not at all sure that gettimeofday() overhead is an issue for libxml2, but 
thought I'd point-out (at the risk of bringing-up something already discussed) 
that a number of platforms seem to have a lighter-weight gethrtime() call that 
can be used to time things.

I suppose that as I get farther along with netperf4 I may see if gettimeofday() 
overhead is indeed an issue.

sincerely,

rick jones