Fix up the autoconf macro to properly use the linker flags for a
statically linked library.

For some reason the running flag being set on the thread initiating the
shutdown did not propogate to the run loop thread. I couldn't find any
memory barrier functions in APR or the FS API so I am using 0MQ to send
a termination request message to the run loop thread.

FS-3794 I think I got to the bottom of the thing you hit with intercept, please update to this version

allow enable_file_write_buffering to alternatively allow you to set the exact size of the pre buffer