added isobc to parameters for new isostasy B/Cs

src/module_definitions.f90

@@ -200,6 +200,8 @@ module definitions
 ! this contains all sorts of parameters used in the code, such as flags, 
 ! convergence parameters, octree levels, ... pretty much all parameters
 ! that are read in the input file.
+! isobc is a boolean value used to turn on/off the use of the modified isostasy 
+! boundary conditions (dwhipp 12/09)
 
    type parameters 
       logical compute_qpgram
@@ -214,6 +216,7 @@ module definitions
       logical calculate_temp
       logical isostasy
       logical flexure
+      logical isobc
       integer nmpi
       integer levelcut
       integer levelapprox