Check for all the RLIMIT_foo constants that we use, and update the limit checks to use the new #define values. Fix a bug where failure of some might lead to incorrect bracketing.

Refs #4010
Grrr....use #if instead of #ifdef

Refs #4010
One more round of sys_limit fixes...sigh

Refs #4010
Ensure that comm_spawn'd procs get user-specified forwarded envars

Thanks to Tim Miller for reporting the regression from the 1.6 series

cmr=v1.7.4:reviewer=jsquyres:subject=Ensure that comm_spawn'd procs get user-specified forwarded envars
Protect hwloc/configure/m4's use of some temporary shell variables

Fix problem reported by Paul Hargrove:
http://www.open-mpi.org/community/lists/devel/2013/12/13519.php

cmr=v1.7.4:reviewer=brbarret