Environment-sensitive MPI for hood.math

This commit amends the 'hood' system-sepcific makefile to use the MPI
libraries loaded from the user's shell profile.  This is handy because
hood.math supports multiple versions of OpenMPI, which need to be used
consistently.

Now, the makefile generation process on hood locks in the MPI version
**when the makefile is generated**.  This should carry through in using
the makefile-specified MPI version at compile time, but if the user's
environment is inconsistent they'll encounter a runtime error.

systems/hood.sh

 #!/bin/bash
 
-# System-specific settings for hungabee.westgrid.ca
+# System-specific settings for hood.math
 
 CC=icc
 CXX=icpc
-LD=mpicc
+LD=icpc
 
 # System-specific compiler flags
 SYSTEM_CFLAGS=
@@ -26,11 +26,11 @@ EXTRA_OPTIM_LDFLAGS=$EXTRA_OPTIM_CFLAGS
 # Library names/locations/flags for MPI-compilation.  This will
 # probably not be necessary on systems with a working mpicc
 # alias
-MPICXX=mpicc
+MPICXX=icpc
 MPI_CFLAGS=
-MPI_LIB=
-MPI_LIBDIR=
-MPI_INCDIR=
+MPI_LIBDIR="-L${MPI_LIB}"
+MPI_LIB="-lmpi"
+MPI_INCDIR="-I${MPI_INCLUDE}"
 
 # Library names/locations for LAPACK
 LAPACK_LIB="-lmkl_intel_lp64 -lmkl_core -lmkl_sequential -lpthread"