Added slurm_shutdown RPC.

Addes slurm_shutdown RPC.

modified srun_emu.pl to follow new task launch design
updated port number in testsuite/slurm_unit/slurmd/task_launch-test.c

it now continues to service request even after a failure to completly receive a request

function now handles recv_len ==0 case and returns a error
recv is sending EOF with the 0 return code because the other side has closed the socket

tasks: purge defunct job table entries, run the scheduler, timeout
jobs, and save state (stub for now).

fixed unpackmem were 16 was passed as uint16_t *
added #define for credential signature length

moved a few more signal calls to posix standard sigaction

   to assert(sizeof(*size_valp) == sizeof(uint16_t)) which should catch
   more coding errors.

Updated comments in slurm_protocol_api.h

A lot of little changes

   HAVE_WORKING_STRERROR_R, check for both.

Moving to new task launch design

changed credential.signature from a uint32_t to char[16]  128 signed sha1

job_script is no longer a member of the job_rec struct

Added read/write data structure locks for all RPCs.

on slurm error. Parsing error prints message right away and returns zero.