Code changes to handle SoilWat being repeatedly called as dynamic library

SW_SoilWater.c
	06/24/2013	(rjm)	made temp_snow a module-level static variable
(instead of function-level): otherwise it will not get reset to 0
between consecutive calls as a dynamic library
						need to set temp_snow to 0 in function SW_SWC_construct()
SW_Weather.c
	06/24/2013	(rjm) 	made 'tail' and 'firsttime' a module-level static
variable (instead of function-level): otherwise it will not get reset
to 0 between consecutive calls as a dynamic library
						need to set these variables to 0 resp TRUE in function
SW_WTH_construct()
SW_Flow_lib.c
	06/24/2013	(rjm)	made 'soil_temp_error', 'soil_temp_init' and
'fusion_pool_init' into global variable (instead of module-level) and
moved them to SW_Flow.c: otherwise they will not get reset to 0 (in
call to construct) between consecutive calls as a dynamic library
SW_Flow.c
	06/24/2013	(rjm)	added 'soil_temp_error', 'soil_temp_init' and
'fusion_pool_init' as global variable
						added function SW_FLW_construct() to init global variables
between consecutive calls to SoilWat as dynamic library
SW_Control.c
	06/24/2013	(rjm)	added call to SW_FLW_construct() in function
SW_CTL_init_model()