additional check in configure.ac for flt model
Add flt model

model_flt_calc.c not yet implemented
add model_flt_calc.c and check program
add test function which checks attenuation of sine funcs
allow user to override default CFLAGS
fix all (?) whitespace errors in tree
'make clean' removes #*# files
add flt model to mpi_makemap

* new command-line args
* initialization code for flt model
* set model=com,flt,ast in test script
fix bug in init_model

Previously forgot to initialize model->model_fit to zero. For some reason
this didn't cause problems with com and ast, but does cause problems
(introduces nans into data stream) with flt.