Switched request file write to a parallel write (one file per region).

Replaced serial request read with parallel request read.

Fixed up the reading in of the new cem model

Switched request file write to a parallel write (one file per region).

Replaced serial request read with parallel request read.

Fixed up the reading in of the new cem model
Cleaned up merged version of model_cem.f90 a bit.
Brought model_cem back up to fortran 2003 standard.
added a comment from Daniel Peter
fixed one line typo in smooth_sem utility
Switch xlf to -qstrict.

This change prevents some minor differences of results between xlf and
other compilers. There is a small decrease in performance, but generally
it can be overshadowed by other problems like slow I/O.
Increase iterations for xi and eta to 5.

This should produce consistent results when comparing ifort, gfortran
and xlf.
added a comment about -qstrict
Merge branch 'ak135-consistency' of github.com:QuLogic/specfem3d_globe into devel
"Buildbot ran code beautifier."
updated the comment about increasing the number of iterations from 4 to 5
avoids compiler warnings and adds parameter statement to LDDRK constants; needs a workaround in compute_forces_outer_core_Dev.F90 because of a gfortran OpenMP bug
improves minimum required gpu memory estimate
includes a fall-back option in model interpolation
adds flags in constants.h to suppress mesh stretching for 3D moho/410/660 surfaces
timestep and layers fix for asymmetric 1-chunk simulations
updates interpolation tool by adding separate flags for separating elements on 410/650 and moho discontinuities
updates smoothing routine, adding debugging option; moves and renames interpolate_model_kdtree.f90 to src/shared/search_kdtree.f90
updates smoothing tool using a kd-tree search; updates kd-tree routines; moves heap sorting routines to file src/shared/heap_sort.f90
updates routine recalc_jacobian_gll3D() using debug flag for explicit checks