signal handling in MT

[Sam S. <sd...@gn...>]

Vladimir,
my last patch broke MT builds - it turned out that the SIGTERM (et al) handling 
is not done in MT.
this is not good: bug#2795278 & bug#1871205 have now resurfaced in MT.
why can't we use spvw_sigterm as is in MT?
the only necessary change is that we would have to print "Exiting on signal" in 
all threads, so all we need to do is to interrupt all threads.
Thanks.
Sam.