Revised peos_init.tcl to source kernel's version first.

The installation procedure copies os/kernel/peos_init.tcl to
kernel_init.tcl, which is then sourced from ajax-cgi/peos_init.tcl.
This means any changes to the kernel's peos_init.tcl (which happens
every time the predicate evaluator is modified) will automatically be
included by ajax-cgi/peos_init.tcl.

These changes were necessary to get diabetes_assessment.pml (which
added) to run.
Added pmlcheck cgi program and minimal ui page to ui/ajax-cgi.

This allows one to submit pml code or upload a pml file for analysis.
As a side effect, refactored some common code into ui/ajax-cgi/util.[ch].
Fixed cgi output and added some commentary to input page.
Normalized events.c:peos_run() error messages.
Resolved merge conflict.