Added a C-API lock for Nokogiri.
Added a C-API lock for Nokogiri.

This makes whatever the issue is in

https://github.com/sparklemotion/nokogiri/issues/1047
https://github.com/rubinius/rubinius/issues/2844

to not manifest during more than 1 hour of 100 threads running in
the repro script in the Nokogiri ticket.

If a bug never appears, does it exist?

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