Use SIG_DFL instead of 0

Those are the same on my system, except that the former is defined by
POSIX and the latter is undefined behavior.
Ghetto JIT 0.1 - works
Add autoconf option for JIT support
Run bootstrap
Continue working on FParser JIT

* Path fix for Linux
* Add optimizer opcodes, fix bugs
* Vastly expand JIT opcode support, fix AD bug... oops!
* Add JIT support for if(a,b,c) control flow opcodes
* Make compares fuzzy using Fparser's epsilon
* Fix compile error when fpoptimizer is disabled
* Enable support for more Value_t types
* Fix stack recover bug, add test/example
* Add performance test code
* Fix another AD bug involving cDup
* Tweak/expand tests
* Put JIT cache files into subdirectory
Updating refereces

* Huang 2014
* Schunert, 2015.
* van Rooyen et al, 2014.
Add option for libMesh handling of SIGSEGV

This can be useful for getting stack traces
Merge pull request #353 from libMesh/enable_segv

Add option for libMesh handling of SIGSEGV
Print traces on all processors if requested
do not implement the nonblocking receive_packed_range without MPI, as we axed the prototype
Adding Hansen, 2014 preprint.
Remove DOS line endings from sha1.{cpp,h}
Delete tab characters from fparser.m4
Remove trailing whitespace in fparser Makefile.am and new example source files.
Merge branch 'fparserjit'

See also #349.

I fixed a couple whitespace things before merging by hand.
Be more consistent with number of digits and rounding in new
Gauss-Lobatto quadrature rules.
Update traffic.
Parallel constraint calculation on SerialMesh too

This will hopefully be a speedup for everybody, but more importantly
it should fix a bug where FEMFunctionBase boundary conditions could
not be used on a SerialMesh on more than one processor.
Fix a second place where Qhull injected ambiguous types into the std namespace.

See also d048dbe65a.
sha1.h, not .hh