These functions are intended to do the same actions of sx_xlock() and
sx_slock() but with the difference to perform an interruptible sleep, so
that sleep can be interrupted by external events.
In order to support these new featueres, some code renstruction is needed,
but external API won't be affected at all.
Note: use "void" cast for "int" returning functions in order to avoid tools
like Coverity prevents to whine.
Requested by: rwatson
Tested by: rwatson
Reviewed by: jhb
Approved by: jeff (mentor)
f9819486e5