- Stop calling libthr alternative as it's now the default   threading library.
- Stop calling libthr alternative as it's now the default
  threading library.

- Now that libpthread is a symlink, it's no longer possible
  to link applications with libpthread and have libmap.conf(5)
  select the desired threading library; applications will be
  linked to the default threading library, libkse or libthr.
  Remove an obsolete paragraph.

- Mention that improvements can be seen compared to libkse.

Reviewed by:	deischen, davidxu

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase