Properly lock around signal handler thread
Properly lock around signal handler thread

This problem could cause multiple signal handling threads. When multiple
threads were exec'ing, they would all request starting and stopping the
signal thread. Because we weren't locking this properly, it could happen
that two signal threads were starting which causes all kinds of other
problems such as deadlocking.

jemc/rubinius,pH14/rubinius,sferik/rubinius,jsyeo/rubinius,Azizou/rubinius,Wirachmat/rubinius,dblock/rubinius,jsyeo/rubinius,kachick/rubinius,ngpestelos/rubinius,Azizou/rubinius,pH14/rubinius,mlarraz/rubinius,ruipserra/rubinius,benlovell/rubinius,benlovell/rubinius,dblock/rubinius,sferik/rubinius,sferik/rubinius,kachick/rubinius,benlovell/rubinius,jemc/rubinius,ruipserra/rubinius,digitalextremist/rubinius,ruipserra/rubinius,kachick/rubinius,sferik/rubinius,jemc/rubinius,kachick/rubinius,digitalextremist/rubinius,jsyeo/rubinius,Wirachmat/rubinius,jsyeo/rubinius,heftig/rubinius,ruipserra/rubinius,dblock/rubinius,pH14/rubinius,kachick/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,jsyeo/rubinius,benlovell/rubinius,benlovell/rubinius,jsyeo/rubinius,kachick/rubinius,mlarraz/rubinius,Wirachmat/rubinius,digitalextremist/rubinius,ngpestelos/rubinius,heftig/rubinius,pH14/rubinius,mlarraz/rubinius,jemc/rubinius,mlarraz/rubinius,pH14/rubinius,Azizou/rubinius,jemc/rubinius,mlarraz/rubinius,sferik/rubinius,ngpestelos/rubinius,digitalextremist/rubinius,jemc/rubinius,dblock/rubinius,sferik/rubinius,benlovell/rubinius,ngpestelos/rubinius,Azizou/rubinius,pH14/rubinius,digitalextremist/rubinius,Azizou/rubinius,sferik/rubinius,mlarraz/rubinius,ruipserra/rubinius,ngpestelos/rubinius,kachick/rubinius,digitalextremist/rubinius,ruipserra/rubinius,Wirachmat/rubinius,jemc/rubinius,heftig/rubinius,jsyeo/rubinius,dblock/rubinius,kachick/rubinius,heftig/rubinius,digitalextremist/rubinius,Azizou/rubinius,dblock/rubinius,Azizou/rubinius,mlarraz/rubinius,dblock/rubinius,ngpestelos/rubinius,heftig/rubinius,benlovell/rubinius,ruipserra/rubinius,pH14/rubinius,heftig/rubinius,Wirachmat/rubinius,Wirachmat/rubinius,heftig/rubinius