Add a new kernel compile debugging option, DEBUG_CRIT_SECTIONS. This fairly

Add a new kernel compile debugging option, DEBUG_CRIT_SECTIONS.  This fairly
invasive debugging option compiles matching code into the critical section
inlines and reports mismatches at run-time.   It is used to detect
missing/forgotten crit_exit() calls.

Note that because there are a number of places where critical sections are
manipulated outside the procedures that entered them, this code will
generate a number of false hits and should only be used under the direction
of experienced developers.

Note that the thread structure will be extended by this option.